Haven't played her much recently, but I used her a lot when Sm4sh was new. I just really love that charge shot. Her overall gameplay is really weird. I basically consider her a tertiary character. Every other character in this part of the list is mostly casual since I haven't had the time to try to get very good with them yet.
Shulk I just really like his style, his long range, and his arts. I probably won't play with him in Smash 4 anymore since Smash ultimate will fix my problem with him. Though I definitely played quite a bit. I usually did pretty well despite not doing some of the fancy stuff that shulk mains do.
I gotta say people saying that Ganondorf is the worst makes me interested in him since it makes him abit of an underdog, and he's so fun to play with. Also, while other characters can kind of do what they want a bit and not pay as much attention to the opponent, Ganondorf requires you to pay attention to do well.
Ike is similar to Ganondorf, but a bit easier to use, and much simpler. I really like fighting Ike players more though.
Speaking of underdogs, Little Mac's character is basically all about being an underdog. He's also really fast, so I love playing him. A lot of people underestimate how scary Little Mac can be. Whenever I start neglecting my ground game, I switch to Little Mac for a bit to force myself to not auto-pilot by going into the air.
Robin is a magic/sword user. His gameplay just feels good all around. Just he feels a bit slow at times, and that limited use mechanic is a pain.
Then of course I sometimes just pick a character to do shenanigans with. Seeing how well I can do against an opponent using Falcon Punches or Game and Watch's 9 is a fun thing to do when I don't care about improving at the moment and just want some time to screw around. There are characters I want to put on this list, but really, I don't play them enough to bother mentioning. There's only so much time to play each character.