Low:
1 - Goomba (Mario)
2 - Deku Scrub (Zelda)
3 - Ghost (Pac-Man)
4 - Infected (Half-Life)
5 - Grunt (Halo)

Middle:
1 - Splicer (Bioshock)
2 - Undead (Dark Souls)
3 - Reaper (Mass Effect)
4 - Darkspawn (Dragon Age)
5 - Sith (Left 4 Dead)

High:
1 - Tyrant (Resident Evil)
2 - Behemoth (Fallout)
3 - Colossus (Shadow of the Colossus)
4 - Black Phantom (Demon's Souls)
5 - Spartan (Halo)

Low:
1 - Goomba (Mario)
2 - Ghost (Pacman)
3 - Grunt (Halo)
4 - Headcrab (Half-Life)
5 - Skeleton (Castlevania)

Middle:
1 - Locust (Gears of War)
2 - Reaper (Mass Effect)
3 - Wraith (Diablo II)
4 - Darkspawn (Dragon Age)
5 - Undead (Dark Souls)

High:
1 - Spartan (Halo)
2 - Jedi (Star Wars)
3 - Behemoth (Fallout)
4 - Colossus (Shadow of the Colossus)
5 - Deathclaw (Fallout)

@Machina

No Sith

On Topic:

Low -

1. Goomba
2. Skeleton
3. Raider
4. Infected
5. Grunt

Middle-

1. SITH!!
2. Reaper
3. Locust
4. Splicer
5. Helghan Trooper

High-

1. JEDI !!!
2. Behemoth
3. Big Daddy
4. Colossus
5. Spartan

Low Ranks 

Goomba (Mario)
Zergling (StarCraft)
Peon (WarCraft)
Grunt (Halo)
Raider (Fallout)

Middle Ranks

Koopaling (Mario)
Helghan Trooper (Killzone)
Locust ( Gears of War)
Wraith (Diablo II)
Splicer (BioShock)

High Ranks 

Colossus (SotC)
Behemoth (Fallout or Final-Fantasy :P)
Tyrant (Resident Evil)
Spartan (God of War)
Big Daddy (BioShock)

I posted this in the other thread:

I'd like to request a few more additions, because I feel like there aren't enough franchises included. I also would like to request that each series only be representable once (so none of this "oh hey, let's put Halo and Fallout into the running twice!" crap).

Other additions:

Low ranks:
-Deku Scrub (Zelda)
-Metroid (Metroid)

Middle Ranks:
-Herobrine (Minecraft)
-Creeper (Minecraft)

High Ranks:
-Nemesis (Resident Evil)
-Tyrant (Resident Evil)

1 - Peon
2 - Raider
3 - Goomba
4 - Deku Scrub
5 - Zergling

1 - Splicer
2 - Wraith
3 - Undead
4 - Helghast Trooper
5 - Reaper

1 - Behemoth
2 - Jedi
3 - Colossus
4 - Tyrant
5 - Black Phantom

If I may, I would like to throw Black Phantom into the ring for high tier

Thanks for taking some of the suggestions.

@Machina

yayy thanks for adding Sith!!!!!

Editing my post

High priority to low:

Low Ranks -
Deku Scrub (Zelda)
Goomba (Mario)
Headcrab (Half-Life)
Zergling (StarCraft)
Ghost (Pacman)

Middle Ranks -
Hunter (Left 4 Dead)
Reaper (Mass Effect)
Wraith (Diablo II)
Locust (Gears of War)
Splicer (Bioshock)

High Ranks -
Tyrant (Resident Evil)
Jedi (Star Wars)
Colossus (SotC)
Behemoth (Fallout)
Big Daddy (BioShock)