I'm a random, but IMO Falco is easier to get the hang of and do well, but harder to master.
IIRC Falco places more consistently in the top 10 than Fox in tournaments, IE. Jman Lucky vs Zhu, Shiz, Dr PP, Mango
I think Falco is just easier to do well with if you know what you're doing. He has a lot of things that lead into other things, such as his lasers and combos. Fox has sheer strengths, like speed, power, etc, but IMO in a real life match, it's harder to utilize/combine those than Falco.
Sheik is annoying. Although I think Sheik gayness is easier to avoid than Falco offence.
Marth vs Falco is very stage dependent I think.
Fox vs Falco, Falco handles Fox very well. Easier to combo a Fox than Fox to get you offstage and gimp you
IMO in a borderline-TAS skilled world:
1. Fox
2. Sheik
3. Marth
4. Falco
In a realistic world:
1/2. Falco/Sheik
3. Marth
4. Fox
If you can get better than Zhu, Mango, Dr. PP, etc., I think playing Fox would get someone farther. If they're close in skill, I think Falco is the way to go.
But we all know Roy is the best character in the game.