sliding a rail nice and smooth is probably one of the better feelings out there, but i still prefer to be in the air. i just keep my shit simple on rails. smooth, stylish, and that's that.
as for jumps, i find the feeling of progressing is so much more satisfying when you stomp that new trick you've been working on. i find it's so much more of a rush too. more sketchy, bigger bails, harder impact, but more glory in the end.
don't get me wrong, people bail hard on rails too, but they tend to be more the bone cracking type of bail as opposed to the bone smashing type (or at least in my experience)