I know this may sound corny or not very helpful at times. But hear me out.
1) I "dated" a lot of the mid/top tier characters. *Dating* - Playing with them to figure out which character gives you the best technique and feel.
2) In my opinion, its always a good idea to have 2 mains. That may sound stupid coming from me, a new player. But, just incase you have a bad match-up, it's always good to have another character to go with.
3) The way I found my main, was from motivation. (I know this sounds weird) Basically I love Marth and Pikachu. Marth because of some old matches I've watched back then. (Ken combo etc) and Pikachu because I've always used Pikachu in Pokemon games and I have multiple plushes etc.
Sorry if this didn't help, I tried xD Hey uh, if you wish to talk to me, add me on skype. - vincentmk8