This has been a pretty well unheard of thing that has been devoloping for some time that has the potential to change the PC gaming market. The program is called "OnLive". And similar to PSN, and Xbox Live, you will be able to try demos for games and things. But the great thing about it is that you will need need to download these games, you instead stream them from their servers. You will also not need a great computer you get great graphics from games, just a good internet connection. If it works as well as I hope then I won't need to worry about upgrading my PC anymore, check it out and tell me what you think guys.
PC for sure, although it is at times not as convenient and as stable as consoles such as Xbox and PS3, you cannot beat the mods that you can find for free for your favorite games. I know that playing Fallout 3 for the 4th time was like playing it for the first with all the mods I put on it. But besides that, if you are proficient with computers and have the money to do so, you will never find better graphics on anything other than the PC. And my last point would also have to be how FPSs are better with a keyboard and mouse in hand, and RTSs not near as good without a mouse to use.