I'm sticking to the newcomers and still don't know who I prefer right now.
I love Wii Fit Trainer from a design/concept point of view but he's pretty limited and doesn't fit my play style as well as I hoped. Still in my rotation and my most played character, but probably not my eventual main.
I was most excited about unlocking Duck Hunt, but I actually LOVE Roy/Bowser Jr. I'm still trying to get much better at him, his kill moves are all a bit tricky.
Greninja is amazing, but I need to improve at his combos and abusing his off stage game.
Villager is really really fun but feels very match-up dependent at times.
I still want to learn Robin, Rosaluma, Pac-Man, Palutena and Shulk better
To give it a try:
Veteran Fav: Yoshi, Jigglypuff
Veteran Least Fave: Falco
Newcomer Fave: Greninja, Roy/Bowser Jr.,
Newcomer Least Fave: Dark Pit