I mained G&W when I played with my friends (tried Wolf, ROB, Dedede, Snake and MK beforehand) but I used Puff to humiliate my noob friends.
I started competitive Melee but also entered Brawl for the lols with G&W and Puff. Later I tried to take Brawl seriously and used DK, Mario, Samus, Yoshi, Sheik/Zelda, ZSS, etc... You get the idea.
I picked up MK to abuse the lack of a LGL in my state, and just stuck with him while I improved my Puff on the side.
After MK was banned I tried to learn ICs, Pit Wario, Martha and ROB. Eventually I fell back on Puff and I'm using her completely seriously for the first time.
There are a lot of characters I am good enough with to use competitively now: Most of the characters above, Bowser, Sonic and Zelda.