For me it's a dead heat between IV and San Andreas. Many others have posted the various strengths of each, so I'll just post my favourite moments that made them amazing.

Miranda's ass, actually.

I have this on XBOX and find it difficult to go back and play. The atmosphere is still there, but the camera almost feels disorienting and the controls are way too clunky. SA was a subtle but monstrous step up in those departments.

I would have called this a statement with a lot of conviction had it not been for the ridiculous overuse of swearing. Grow up.

Yesterday they released songs by the Allman Brothers, The Band, Dragonforce and NIN.

Yeah! With Alaister! And Leliana! And, um.... that elf guy! And... what's her name. The one that's in the first one and looks different in the second one. And Captain Janeway!

Um.... Ashley?

Veh.

Meh.

ASSUMING CONTROL.

The storm outside the Shadow Broker's ship in Mass Effect 2. Outstanding.

Back in high school a bunch of us got together and ordered 100 hamburgers on 49 cent day. It was amazing.

And your wager... Texas with a dollar sign.

Sometimes I feel like the entire run is a setup for the naked fight between Tony Stark and Guy Smith.

Mike Allred, who drew the greatest X-Men series that no one read.

Benedict Arnold? You mean that British hero? Go Benedict!

You know.... whatshername. The one with the mirror.

Nintendo Wii U: "made for kids BY kids!"

Does Chara attempt to kill people using stanchions in the game as well?

RE5 wrapped up things so nicely. *SPOILER* Albert Wesker getting his head blown off by a rocket launcher screamed "it's over."