I've got the 360. Prior to this I was a PC only type. Then I bought the PS2 and absolutely loved it.
Game selection is a bit more limited than the Sony machine(s).
However. The price is much less than that of the PS3. In addition, the xBox works in conjunction with Media Center PC's (or Windows XP service pack 2) and allows you to play MP3's, watch cable/local TV (if the host PC has a TV tuner card less than $100 in most cases), and can even function as a TiVo unit with said TV tuner card and a little extra room on the hard drive of the PC. It can go wireless, meaning that you can do most of that without running wires to the 360. It's also VERY USB friendly. For example. I purchased a multi-card reader for my phone memory card and my camera memory cards (different types). I plugged that into the 360 and it was able to read the media as if it were a jumpdrive or flash drive... very slick.
I watch TV on my TV via the 360 and use the guide I download from the internet (via Media Center) to find whats on and even set up things to record while I'm gone. The 360 does not have to be on to actually record on the PC.
It's a very versatile machine. I'm extremely happy with it.
I can't speak to the PS3 any more, as I've stopped worrying about it after making the 360 purchase and I'm not up to date.