Top row: I really want to be good at these guys. Ness has been my main for most of my time playing any version of Smash, and I really don't see that changing any time soon. He's from one of my favourite games of all time and I love his play style. If I had to answer with just one main, he'd be it, no question. Greninja is one of the best Pokemon designs ever, his play style also looks ridiculously fun and his Smash trailer was one of the best out of all newcomers'. Pokemon X/Y were also the first Poke games I enjoyed in a really, really long time. Finally, Robin also comes from one of my favourite games of this gen, and despite his/her style being a lot more elaborate than the others', I honestly want to be good with him/her. He/She's the character that intimidates me the most in regards to difficulty curve of all I want to play.
Second row: My interest in these characters has risen recently; Pikachu and Villager because of the demo (Villager's tree mind games are freaking nuts, I love him/her), Larry because his play style looks fun (and annoying as hell for his opponents), and Kirby because he's been my "other main" for all past iterations of smash, plus I love his franchise.