The PC version of Grand Theft Auto 4 is unquestionably the best version of the game. Why? Mods. The still-active modding community has added a number of incredible features to Rockstar's open world. iCEnhancer, for example, makes the game look awfully pretty.
Rockstar has yet to announce a PC version of GTA 5, much to the chagrin of PC gamers everywhere. Of course, the modding community isn't going to sit still. In fact, someone's already working on retrofitting one of the sequel's new features back into Liberty City.
In GTA 5, you'll be able to switch between any of the three main characters at any time, no matter where they are in the city. GTA X Scripting (via Destructoid) is attempting to introduce that feature into GTA 4, by having 1, 2, and 3 hot-keyed to three different playable characters: Niko, Johnny, and Luis--the latter two being the stars of the Episodes from Liberty City DLC expansions.
When not being controlled, the two other characters will "wander around" and even evade the cops. It's an interesting tweak, one that will give PC gamers just the smallest taste of GTA 5.