It all depends on how much work you want to put in learning a new playstyle.
easy way: Fox/Wolf.
I've been doing this since the start, they have similar dynamics to Falco's playstyle, the most difference is in the application of their moves. Then again, they also have similar weaknesses.
not so easy way: Marth
Marth, at least for me, is relatively easy to pick up, although using Marth with competence will take some practice. The playstyle is drastically different, and offers some relief against characters that would give Falco a headache.
the hard way: Snake
Nothing about a well-played Snake is simple; multiple projectiles at your disposal, land mines, mortars and C4, even a box. If you are willing to put in the time and effort needed to learn this bizarre playstyle, you will have a really dangerous alternative to offer your opponent. Snake is heavy, powerful and chock-full of goodies to explode on your opponent, characters that do well against Falco are often little trouble to an equal Snake. if you are looking for different, Snake has it in excess, Just know that Snake's playstyle is really tricky to learn for someone who doesn't use him a lot.
