Jump physics are indeed a careful balance. It's an incredibly important part of this elusive thing known as "game feel". A fair number of people seem to think this term is bullstuff, but it's actually really important. A game that controls or feels bad effectively is bad.
On the other hand, it also has a lot to do with the type of game you're making. If it's more fast-twitch action, you probably want quick, sharp, tightly-controllable jumps, as in Mega Man. If it's more laid-back platforming, you'll probably want physics that are inherently more fun to control, as in Mario. You can get away with significantly floatier jumps, but it's important to pair this with acceleration-based movement and a lack of airborne friction. Still, no matter the game, if jumps are too floaty or too fast, the game is going to end up frustrating to play, and that's the last thing anyone wants.
Just my two cents.
