I prefer my PS2. I personally have not had the chance to own a PS3 but played one enough to realize that none of the games really appeal to me. I love RPG games and PS3 doesn't really seem to have those. (I am a big fan of Kingdom Hearts, Final Fantasy and the .hack games)
PS2 games because of nostalgia. I miss the old times when I used to have 1561069 games, and invited friends to play with me every week... But in general, PS3 is better. I just don't play it like before