PS3 - Absolutely horrible online play, if you're looking to keep friends and communicate easily. The games are good, the only new thing about them is six-axis and new graphics. Oh, and fancy BluRay.
Xbox360 - EXCELLENT online play. Communicate with friends via mic, text, answering machine, and more. Do that all even if you're offline or in a different game. The offline gameplay is the same as the PS3, nothing new, but better graphics.
PC - Always something new to do. Code, play games, hack games, community forums, chatting, etc. You can upgrade it, like the Video Card, the Processor, basically keep it updated it everytime something new comes out. If a new game machine comes out, you have to buy a whole new one! A PC, you don't have to buy a new one everytime something comes out. The games graphics are amazing, and will always win over 360 and PS3. The online play is much better, and many more people are playing.
Winner - PC. If you're looking for an all around thing, buy the PC. If you want a PS2 with better graphics, then buy a PS3. If you're looking for a great gaming-only machine, online and off, buy a 360. But I still think PC is more worth it.
Hope I helped

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