thats a hard one and VERY subjective
from my personal opinion (which will be strongly dissagreed with i hope)
gamecube - best current console, a smallish library of superbly playable games and a few of the usual multi fort dross titles that blight most systems (although several have (like the xbox versions) a few graphical enhancements over the ps2 versions, but backups are not GENERALY around YET
xbox - dead easy to chip, realy requires you to have a dvdr drive for your backups, sadly absolutly nothing commercial worth getting, the games are all of a poor standard (although a few are very pretty i'd hate to think of the last time my kids played anything on the xbox, although there is a lively homebrew scene.
ps2 - expensive to chip (for games buy a messiah or clone), a vast library of mediocre games and some truely great games, most cd based games can be backed up and played directly as can dvd games if you have a dvdr, a large number of high quality dvd rips can be found on the internet allowing you to play many of you dvd based originals from a nice cheap cdr backup
i'm sure that will only confuse you further, but the best bet is (assuming you can afford) buy a gamecube for its excellent games then buy one of the others (chipped) to collect the dross (xbox has more potential than ps2 but ps2 has better games at the moment)
ABCMan