A short-midranged powerhouse, Saber is versatile and can fill a variety of roles. While certain servants are limited to attacking or defending, Saber is able to do both at once. With Invisible Air and Caliburn to fend off nearby foes, Excalibur to smash away incoming enemies and Avalon to counter high damage spells, Saber is certainly a servant you'd see often. She is capable of protecting from Jumpers like Lancer and Rider with Avalon, providing long ranged support with Excalibur and even assisting close range with Caliburn and Invisible Air.
One of the more useful servants in attacking, Archer boasts one of only two Far Sight spells in the game(And the only one that can detect invisibility), granting sight of far-away locations without the need for Owls or Sentry Wards. This is often a huge advantage in team games and especially Arena, where an Archer with Clairvoyance can hunt for wards easily. His Caladbolg ability allows him to stun a target for 2 seconds at a long range, making it one of the most useful stun abilities in the game. Unlimited Blade Works is also undoubtedly one of the most deadly spells in the game, dealing physical damage instead of magical, bypassing Magical Scrolls.
Lancer is one of the best damage dealers in the game, with his two Gae Bolg spells allowing him to deal high spike damage while also having defensive abilities that allow him to survive for a long time. The first Gae Bolg, The Piercing Spear of Death is capable of executing Criticals , doing double damage or triple damage. These unexpected bursts of damage can often take down enemies or severely weaken them. The second Gae Bolg spell, The Flying Spear of Striking Death, is one of the largest area of effect damage spells available in the game. While its range is not as high as Bellerophon, it certainly has a larger area of effect to work with. With support attributes like Protection from Arrows and Battle Continuation, which allows him to resurrect after taking a 300-1000 or 200-1200(with attribute) damage hit with either 1 or 25%(with attribute) hp, he is a difficult servant to take out.
Rider's Bellerophon is among the highest damage spells in the game, dealing 2100 damage at level 5 with the Riding attribute. This, coupled with short warning time and the unpredictability of its animation makes her extremely deadly. Rider is also a useful hero when it comes to support. With her Catena Sword Nail to interrupt enemy spells, Breaker Gorgon to slow and an Upgraded Blood Fort Andromeda capable of both interrupting and slowing, she is one of the more irritating servants. Furthermore, she has a chance to paralyse enemies with Stone Form, which renders an enemy helpless for a few seconds, often resulting in their death.
Caster is a dedicated support character, with her Sacrifice spell granting invulnerability to allies and her Rule Breaker doubling magical damage on the target. Truly one of the best support characters in the game, Caster can save people from sure death, as well as preventing enemies from attacking with Silence. She is also able to create scrolls, a very useful ability, while her Upgraded Territory Creation skill grants her a Far Sight spell. While one could see her as a servant that is restricted to pure support, this isn't quite true in practice as Rule Breaker can prove to be fatal when combined with Lightning Rain/Bombing and/or S or EX scrolls.
Compared to other characters, the False Assassin does not have any mass killing skills such as Gae Bolg or even a powerful spell like Bellerophon. However, False Assassin is one of only two characters in the game that can do Pure Damage - damage that cannot be reduced by anything except for Spirit Link Scrolls and Rulebreaker. This is often useful as A and B Scrolls are used to provide protection but are ignored by Tsubame Gaeshi. False Assassin can also act as Sight for a team, with his Mind's Eye attribute granting sight of nearby enemies for a few seconds, while his combo summons four illusions to fight for him can also be used to scout out enemies.
Berserker is a tank if there ever was one - He has the highest starting HP in the game (1600), gets massive amount of strength naturally and even reduces attack damage. With his God Hand attribute, he can even resurrect himself upon dying, in addition to Berserk which locks his health to a fixed amount for a period of time. He is also a hard hitter, with Courage to reduce the armor values of his enemies, as well as having Chaos-type damage, dealing 125% to all armor types. However, he takes extra damage from Enkidu and Arrow Rain. His Nine Lives ability holds an opponent in place for a few seconds, allowing precious time for allies to kill the stunned person.
Gilgamesh tends to be one of the richest heroes in the game - his Golden Rule attribute grants him 1.5x gold per hero killed, while he also has an income of 10 gold per second. This means that you can ask him for gold if you run out, since he will almost certainly have some to spare. With his Enkidu ability, he can hold enemies in place for up to 4 seconds at lvl 5, an invaluable skill for assisting allies and setting up kills. Enuma Elish is also the highest damage regular spell in the game, at 2600 damage without any need for attributes, while his Gate of Babylon ability pierces through Anti-Magic potions and B Scrolls.
True Assassin is one of those heroes that can easily spook other players - he can come out of nowhere and kill someone and be gone again before you can catch him. With his invisibility skills, he can stay out of sight and use his Noble Phantasm, Zabaniya to do up to 1800 damage at level 5, which is almost a guaranteed kill on low-health heroes. He also has an instant-cast ability, Steal, that has a chance of stealing an item, while always stealing a certain amount of gold. This can prove to be extremely irksome when you're low on gold. Along with all that his Self Reconstruction can be continually used with enough mana regen to allow for bonus stats boosting his stats based on luck.
Dark Saber is a servant that can tank very well, while still being capable of doing massive Area of Effect damage with her spells. She can prove to be one of the most irritating servants to kill, with her Improve Mana Magic attribute granting her additional armor and Magic Resistance. With her attribute Mana Blast she gains access to Mana Orbs which can deal +1400 damage when she uses her W with 7 orbs. Max Mana Blast, her combo, deals damage according to her maximum mana, which means that she can do up to 2044 damage in a huge AoE(1500). Dark Excalibur also ties with Enuma Elish for the highest damage regular spell at 2600 damage with the Empower Darkness attribute, while having longer range than Enuma Elish.
Avenger is an odd servant to play - not a lot of health, lacking in damaging spells but has the ability to melee very well. Avenger plays nothing like the rest of the heroes - he can rely on taking damage in order to damage the enemy. His main spell, Berg Avesta, reflects damage(as long as he remains conscious) back to the source up to 2x. His Murderous Instinct gives him additional Mana regen, damage and the ability to stun the target on attack making his melee one of the best in the game. Some of his tanking ability and most of his melee ability will come from his True Form which gives him additional health and bonuses to move/attack speed. While in True Form he also gains the ability "Dust Explosion" which deals damage based on the level of True Form to anyone near himself but it deals 300 damage to Avenger. He can also gain a very interesting ability - Lifeswap, which enables him to trade HPs with his enemy. This means that he can damage himself deliberately, then pop up at the enemy and Lifeswap him, which is almost a guaranteed kill if his health is below 400(The damage of a S Scroll).
Lancelot is quite possibly one of the most versatile heroes in the game - His unique ability, Knight of Honour, allows him to use a variety of noble phantasms that don't belong to him. Among those abilities, he has both Rulebreaker and Nine Lives, allowing him to do some support actions, as well as providing him with a long stun ability for allies. With his Aroundight and Double Edged Sword, however, he can become one of the most fearsome melee characters in the game, with an attribute that enhances his physical damage with additional magical damage, as well as an awesome +45 to all stats and +70 damage at level 5 of Aroundight. Note that Lancelot takes additional damage from everything while using Double Edged Sword, however.
Diarmuid is extremely skilled at incapacitating enemies, with Gáe Buidhe dealing damage that subtracts the maximum HP of enemies, and Gáe Dearg bypassing magic resistance and protection scrolls. With his Double Spear Attack attribute, he can deal up to 1.75k damage, making him a very potent single-target killer and disabler. Crash also enables him to easily enter battle without having to use a blink scroll, allowing him to do damage effectively while still being able to escape. His combo also allows him to do ridiculously high damage with his regular attack, enabling him to kill enemies that haven't upgraded armor in two or three hits.
Gilles has many roles and many play-styles along with having a lot of units to control, making him probably the hardest hero to play properly, from Damage, DPS to suppressing enemy heroes and even supporting his allies. Most of his play-style will revolve around his Territory which can teleport to Gilles and has a DoT that deals damage based on max health and bypasses Protection scrolls/Great Magic. The territory also allows him to heal allies which can be very useful for people inside Nine Lives and etc. Summoning Demons are useful for scouting, dealing damage and laying bodies around the map. His spellbook gives him spells to give itself mana, transfer mana to territory, deal DoT damage to enemy, blind the enemy and turn himself Invulnerable. Corpse Explosion is a very good damage dealer with the ability to deal 2800 damage when 5 corpses and the thrown corpse hits, along with the DoT that happens after, however the corpse exploded is random and the AoE for each one is extremely small. His Demonic Creature has the ability to deal 1400 damage on summon and then has many spells to suppress the enemy heroes, usually resulting with them attempting to stay away from the Demonic Creature. His Combo will deal damage based on max health to the enemy for 20 seconds allowing a big window where the enemy will be weakened to be able to kill them.