Eventually I'll figure out who my favorite secondary is, but right now it's a tossup between:
Captain Falcon, Wario, Kirby, Yoshi, King Dedede, Ness, Bowser, R.O.B., and Marth/Lucina.
I don't feel like anything's missing in Jigglypuff's game, so I take up secondaries for the fun of it and not because I need to counter something. Most of these characters are pretty similar in getting massive value out of one or two aerials that they get started either by using a dash attack or a throw.
Non-energy projectiles are the closest thing to a problem for me (but Puff does better against them than my other characters), though, so if I can eventually get used to the Smash 4 Falco then he has a shot to appear on my list.