Intriguing thread.
I do have to say that it is a combination of both questions listed by the OP, though. I go straight for the jugular in Smash---if I like a character from a particular franchise a great deal, I go for them right from the get-go. I tend to let them go if they don't fit mesh very well with my playing style, however. Bowser in Melee is a good example. Ever since they fleshed out everybody favorite Koopa King in SMRPG, I've had nothing but love for the character (before, I looked at him as little more than a pixellated obstacle that is dealt with by a well-timed jump and an axe at the end of the bridge). However, I couldn't get him to click with me; slow characters aren't really my thing to begin with. I went straight for Sheik after that. I liked Sheik a lot as a character, anyway (or what little there was of Sheik's character, anyway. I always wondered what it would be like to play as her in OoT and Melee gave me my wish. Kinda shallow, but meh). I found that Sheik really clicked with me (and several other bajillion players. lol) and so I stuck with her.
While I haven't had the pleasure of playing Brawl yet, I definitely have to say that my two selections for mains are based off of sheer fandom for the time being. Perhaps my opinion my change when I actually play the characters, but who knows?
Though I was introduced to it rather late, but I'm a pretty big fan of the Kirby franchise. As soon as I saw Metaknight, it was simply love. He oozed cool. I will never forget the fightin Kirby's Super Star for as long as I live. It was simply epic.
Coming at a close (if not **** close to equal) second in the character main priority is Sonic. I can't even begin to tell you how much I like the character. Seriously. I've been a big fan of Sonic ever since I was like, four or five. The Sega Genesis was the first system that I truly owned (preceding that was the family Nintendo lost to the annals of time and space) and Sonic was the first game I played for it. I am sorely disappointed in the craptastic 3-D games that they're coming out with nowadays, but I remain a staunch supporter of the classic and (in my opinion) the most iconic version of the Sonic character. It delights me to see Sakurai pulling so much from the old school Sonic games in Brawl. From Green Hill Zone to even some of his sound effects (which, I swear to God, are pulled straight from the classic Genesis games) to his freakin' voice actor (OMG the dude from the old Sonic cartoons)---they really outdid themselves with the old-school rep.