Fox has a better utilt, dtilt, and ftilt imo (with the utilt of Falco coming close). Fox has a better dsmash and usmash imo, but his fsmash is a little better.
In the air, Fox has a better fair and uair, but a worse bair, nair, and dair. Fox's shine is nothing compared to Falco's, fox's laser nothing compared to Falco's, illusion doesn't spike for Fox... only his Firefox is better.
Also Falco wins in grabs and jabs, which is where I think the game of Brawl is won and lost. Also Fox's super fast fall speed hurts him (as was already said). Fox is not a bad character at all, and I think he will probably move up, maybe even a little bit into high tier. But unlike Melee, his avian wingman is significantly better.
Just for fun, you should play Falco for ~30 matches, and then switch to fox. They are so similar in terms of how they can be played, but their subtle differences make them two very different animals. The slightly faster falling speed causes me to miss illusion sweet spots, his dash grab is timed a little differently...