I have a 360, and I got it because at the time the PS3 was a $700 bluray player with about 12 games. Originally I got my 360 as a means of playing Oblivion (a game which, funnily enough, I'm npt very fond of anymore). Now, I'm glad I have it. I find the XBLA easy to use and has a lot of titles I'm interested in. However, my roommate has a PS3, so I don't find myself particularly limited in terms of selection (other than the obvious limitation of living on a student budget). At this point in the console generation (with me not particularly concerned about multiplayer, or owning any blurays), I don't really think it matters all that much which of them I use.
I don't use a PC to game because I have a Macbook Pro(I did not specifically choose it, it was a gift). I have Windows 7 on boot camp, but I've only used that to play point and click adventure games. With the memory I have alotted, I don't think it would function as an effective gaming rig, and while I could devote more space to the windows side of the partition, I prefer to allot as much space for photoshop and psd files on my Mac side as possible.
As handhelds go, I own a PSP. The PSP attracted me more than the DS because it had more titles I was interested in at the time when I got it. I wanted to play the Dissidia games (which I still do), and Monster Hunter, Crisis Core and a bunch of other titles attracted me to it. However, I'm finding that the DS is looking more and more attractive as my desire for "moar puzzlez!!" increases, it having a large catalogue of games ready to satiate that particular hunger.
So there's my preferences, I guess. Herp-a-derp, I like stuff.