I think all three are solid. They do carry over some problems that people had with the original games, but to change that would change the game itself. However stuff like framerate is steady and it's proper widescreen - not stretched. NiGHTS is not a straight port of the Saturn version, it has more in common with the PS2 release, and I believe the Saturn mode is present. Also, Jet Set Radio has the camera mapped to the right stick.
I'd say NiGHTS is the best one, followed by Jet Set Radio, and then Sonic Adventure 2. But they're all solid releases.