I bought GTA 4 for 360 when it was kinda new... because Blockbuster was selling a used copy and some employee mistakenly put a $10 tag on it, even when 40 to 50 was still the going rate. :-)
Starting with GTA4, I don't play those kind of games on the PC anymore. Aside from all the issues with that title in general, I think the xBox controller is a better way to play, so why not enjoy it in my living room?
That said, I played San Andreas on PC, and I think it not only rocked, but I think it was a better game. More area... three cities and a lot a rural land. So many more vehicles, mini-games, and ways to customize the character. I like 4 a lot, but SA is still my favorite.
Haven't bought the GTA4 expansions yet, but I definitely will.