Never heard "main" until reading threads on Smash Bros. Brawl. Maybe it's a popular term in threads about fighting games that I'm unaware of.
I'll main, from most important to least:
1. Wolf (he had me at *howl*. Seriously. He might even look better)
2. Falco (perfect in Melee. Want to see if he's as fast and nimble as before)
3. Lucario (I'm intrigued. Good-looking, might do kung fu stuff, could be floaty like Mewtwo)
4. Sheik (quick and nimble)
5. Ness (can't forget him. I like his floaty movement and PK Thunder)
6. King Dedede (I can't resist, I just have to see how intimidating he is as a fighter, see if the hammer knocks the stuffing out of everyone)
7. Ike (if he's the new Marth, then sure, why not)
8. Pit (given how much I loved Paratroopa in Mario Tennis for his floaty feeling, and how Ness in the Smash Bros. series is also floaty, maybe I'll like Pit who can actually fly)
9. Luigi (old favorite, although I always felt his attacks were weak. Spamming Down-A was my key to winning)
10. Link (old favorite, fast)
And for the record, I checked the statistics I had on Melee (last time I played the game was 5-6 years ago, youch). Says I played Roy most of all, and Falco second-most. Must be that I was exclusively playing Roy ever since I unlocked him early on (before, I was playing either Sheik or Marth), and that Falco was unlocked pretty late.