Mine is kinda ironic.
I used to main Ness back in Melee, but he wasn't really that good and was also very hard to use correctly, so I started testing Marth and fell in love with his style, combos and that sexy ability to spike super easily.
Now, Marth feels too slugish for my tastes, his tilts and air attacks are just... I don't like em, so I stopped maining him for, guess who, that's right, NESS, which I ABSOLUTELY ADORE, this time around. Just like I abused Marth's Ken combo in Melee, now is down tilt > pk fire > down grab > sh into fair > double jump fair, all day every day. I still use Marth (mostly Lucina) a lot, he's not my number one anymore, so happy with Ness >_<