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It's hard to tell.
I think it really depends on your artistic style and kind of humor.

I guess most multiplayer-games are a good foundation because it's players are often a huge inspirational source,to put it charitably :P
Who doesn't know those team-mates who just annoy the whole team?
First examples I can think of:
PAYDAY: The Heist
Left 4 Dead 2
Portal 2
....

Game: Spec Ops: The Line
Reason: If you can make a humoristic comic about that, you win at life.

Magicka!

TF2. For funs.

what about the binding of isaac?

or a crossover!

Borderlands 2 meets TF2

Binding of Isaac, haven't seen any webcomics of that

Puzzle Agent...because, c'mon, it's Nelson Tethers.

I think its pretty obvious what should be featured...

ArtRage 4, so unique no other webcomic would dare go where you went. You'll be on top of the webcomic world in no time.

Which game? hmm... Maybe hitman + duke nukem that have to survive to a zombie apocalypse (L4D2) D;

Killing Floor has my vote!

Has to be Sleeping Dogs, its the only game in your list that has a ™ after the title!

counter-strike source

Mcpixel or scribblenauts

Binding of Isaac

Organ Trail or Scribblenauts

maybe some multiplayer games?

Maybe make MLP comic to attract big crowd with first strip? :P There is that money-grabbing MLP game to parody...

Batman: Arkham Asylum
Batman: Arkham City
Borderlands
Borderlands 2
Castle Crashers (I know it's the giveaway but could be very funny)
Darksiders
Duke Nukem Forever
Left 4 Dead
Left 4 Dead 2
Magicka (Could see this being amazing)
McPixel
Orcs Must Die! (This would be a good one)
Plants vs. Zombies
Portal (Another one I could see being awesome)
Portal 2
Team Fortress 2
Terraria
The Binding of Isaac

I tried to only comment on games I know and would actually work a bit rather than listing every game you own. Some just would not be funny.

Chivalry Medieval Warfare.

Checked your profile, saw that you have won 74 games, i was like "oh gawd how? D:" then i saw your CV... Thank you very much...

Also! I would like to see Binding of Isaac, or some GTA <- its random moments makes it fun always :D

Dead Space,
Dead Space 2,
Left 4 Dead 2,
PAYDAY The Heist,
Bastion