I liked both. ALthough XD is probably the better game simply due to the longer storyline and more things to do (and a lack of an annoying save function as well), I kinda prefer Colosseum's plot, despite the plotholes (but let's face it - XD also had its fair share if you look). Playing as a protagonist who WASN'T a ten-year-old - or less (coughMichaelcough), was refreshing, for instance. And it just appealed to me as well. Down to personal opinion though, I guess.
But I liked both of them. Miror B was in both too - while IMO his salsa music is the better, he's more active in XD. So they both win. -_-