In general, I like individual facets of Colosseum more, like the plot and the characters, but I like GoD more as a game thanks to a much bigger roster of Pokemon to choose from and a bunch of added new features. Also, the AI is atrocious in both, especially in GoD, so the games are easier than they should be, but eh. It's worth noting that GoD's story mode is much longer than Colosseum's, but lacks the colosseum mode where you can bring in mons from a 3rd gen game and battle with them. I'd play both if you have the time and money, but if I had to pick one to play, GoD is a more fun game with more variety, so I'd choose it. Also, the snag list in Colo is downright awful (with a few exceptions like the legendary beasts, Skarmory, and Hitmontop, plus the second stage of a Johto starter of your choosing), while the snag list in GoD is better and the awful stuff you get actually has decent moves, so you feel compelled to use them at least for the beginning of the game. In both versions, the Pokemon you get will come preloaded with TMs and egg moves, and in the case of GoD, certain moves that the Pokemon would have no other way of learning i.e. Heal Bell Mareep.
