When I look at characters I tend to categorize them by speed, power, or balance, and for some reason I felt a lot more comfortable with a character that had pretty good speed, which is why my Main was Marth and my Secondary was Fox (Marth wasn't as fast as everyone else, but he had a good amount of speed, and his style ended up fitting me perfectly).
So, knowing how awesome Meta Knight Already was, I chose him to be my main in brawl. He has the kind of speed in his attacks that I had been used to back in Melee (When L-Canceling decreased time between attacks a good amount). Plus I mained Kirby in 64, so I was already used to getting in the extra jumps, but the glide option for Meta-Knight made him a pretty cool character to use as well. What almost turned me away from Using Meta Knight was the fact that all of his attacks set him into the 'Free-fall' State, but after using him for a while and figuring all of his B attacks, I Found ways to use them effectively in different situations (not all, but some).
My Secondaries in Brawl are now Marth and Sonic (Ultimate Speed! XD), but I hope to get better more with Marth than Sonic.