I preferred Dawn of Sorrow over Portrait of Ruin, though I don't know very much why. If you enjoy touch screen controls, go with Portrait of Ruin, for one of the extra modes.
If you like online play, or play with friends, Prime Hunters is good, but if you don't, I don't think there's too much of a single player mode there, though I never finished it.
I'm curious to know if the Ultimate Jump Superstars, or whatever it is called, is worth picking up, as someone who has never once imported a game, and doesn't really plan to ever. I feel halfway about it, but can't convince myself to.