this is amazing and I truly hope you continue! totally love every one of these chapters, even if I don't necessarily know the character that well. I'd love to see anything more you post... how about Lina Inverse? :D

I want to suggest Reinhard von Lohengram as F/Z rider. Emperor of the Universe.

A few Suggestions Names and Most likely class:
Assassin: Hisoka (HunterxHunter)
Rider: Judge Dredd
Archer: Hellboy
Caster: Orochimaru (Naruto)

Love this fanfic so far, truly epic and funny. So, my suggestion for a character to write is Clary Fray from The Mortal Instruments series.

Servant: Saber
Real Name: Knight Artorias
Alias: Artorias the Abysswalker, The Abysswalker
Master: Emiya Shirou
Alignment: Lawful Good

Strength: A
Endurance: B
Agility: B
Mana: C
Luck: D
Noble Phantasm: A

Class Skill: Magic Resistance: C
Saber was a strong-willed knight in his time, able to cast minor miracles in his legend with one notable exception. However, after being forcibly corrupted by the Manus and the Abyss, his rank is lowered one level.

Personal Skill:
Abyssal Corruption: E
At the end of his life, Saber was forcibly corrupted by the realm known as the Abyss, the home to primeval man, Manus Father of the Abyys. Thus, he is tainted by the Abyss' corruption. However, while summoned as Saber, he is only slightly affected, as he is summoned from the moment before corruption is significant.

Will of Steel: B
Saber was a knight who lived by his beliefs. His actions never betrayed his words, and he believed and trusted humanity, even when his fellow knights did not. Even in the last moments of his sanity, he sacrificed his Noble Phantasm to protect his companion. However, because of the Abyssal Corruption, his rank is lowered by one.

Noble Phantasm:

Covenant of Artorias: B
In his legend, Saber was accused of forging a covenant with dark forces, and seen as a traitor. The truth however, was that he made no such agreement, but rather made a covenant with creatures of the dark to traverse through the Abyss. This allows Saber to traverse through corrupting areas for extended periods. This can only work once Saber is wearing the ring which symbolizes the covenant.

Great Shield of the Abysswalker: A
Though Saber was unmatched with the great sword in legend, his fame originates from the immense great shield he carried in his other hand. Its magical properties allow it to withstand forces normally deemed unstoppable, and can even be used as a catalyst to create an EX-rank magical barrier. However, to construct said barrier, Saber must sacrifice his left arm and use the barrier to protect one other than himself. This can only be done once, and the effects will be permanent.

There is one Thing I noticed which seems strange. You write that the holy grail is supposed to be the holiest Thing in existence, but nobody in Canon thinks the Holy Grail is actually holy. (It is specifically mentioned that it has nothing to do with the Cup of Christ.) It is just a magical item that was created from Justicia von Einzbern and that Name was given due to its capabilities. Considering the nature of magi and magecraft, almost nobody would think of something created by them as a holy thing even before it was corrupted.

Its a good thing. if Superman didn't kill that bastard might as well give him a fate worse than death, right?

I want to recommend Ryner Lute from Legend of Legendary heroes as berserker in Fate Zero. Or as caster.

As berserker, it'll be cool to see him wipe out fuyuki and all servants out of the physical, spiritual and astral planes of existence while saying stuff like 'Disappear, worms' and 'be crushed, ants'. Oh god, what I'll give to see the look on Gilgamesh as his molecules turn to sand and Ea get destroyed. All the while being called a worm or an ant.

Or as caster, give him the 'solver of all equations'. And have him make an equation to wipe Gilgamesh out of existence, or better yet, all his noble phantasms, including Enkidu and Ea. Other, he can simply wipe out all living beings in Fuyuki with a single thought, though I'm sure he wouldn't that.

PLEEEEEEAAASSSEEEE.
Lina Inverse the Dragon Spooker is awesome! Please put her in!

I could have sword one of his abilities was going to be 'Jump Good'

wow, these are pretty interesting
ok for servants
Sora (KH) as Saber
Vegeta or Asura as Berserker
Amuro Ray (Gundam: Char's counter attack) as Rider
Nahona as Caster
and Goku (Saiyuki) as lancer

Luso Clemens, Marche, or Ramza Beoulve from the final fantasy tactics games

Have you considered Guts from Berserk? He could work as either a Saber or Berserker class.

Perhaps your next chapter could showcase Saitama, aka OnePunch Man. Possibly the only servant more overpowered than Superman.

Elsa from Frozen as Caster