Reasons for:

PS3:
-It will be the most powerful system ever thanks to an amazing CPU called... teh Cell!!!!
-It will have Blue-Ray for watching HD movies.
-Expected to have more JRPGs than any other console (FFVII remake oh **** yeah!!!).
-Release date (in America) is a year after the Xbox 360 = time to save money (but i'll probably not buy it until FFVII or MGS4 come out which won't be until late 2007 or 2008 I suppose).
-I can use my 32mb memory stick that came with my PSP and is now collecting dust (since i'm using a 1gb one for my PSP).

Xbox 360:
-It will produce the best graphics next gen thanks to... free 4x antialiasing (that never ceases to amaze me) and other amazing things that the Ati Xenos GPU can do (48 pipelines my God!!).
-Best controller ever! (the PS3's controller makes me cry)
-It will have more (and better) games than the other systems (for releasing first + easiest to develop for)
-Xbox Live (enough said) + the HDD (we can download demos and trailers of games plus a gazillion other things to do like listen to MP3's on every game, save games, use as cache to eliminate load times, and etc.)

Revolution:
-TSHBO (teh sheep have been owned)