Not a fan of how they've handled Mario's alts in the past few games.
My preferred Mario alt was always the reversed blue/red "Jumpman" one. Smash 4 replaced that with the cotton candy pink/blue "Mario Bros box art" alt, which is a nice reference but to me looks hideous (plus it's a much less iconic look than the Jumpman one).
After losing the Jumpman alt, I switched over to my second favorite alt: the Fire Flower one. Now that seems to be gone, too, along with the classic "Wario" alt as well. Now Mario doesn't have any alts left that I really like. Builder and wedding outfits are cool and all, but I'm more of a fan of nice-looking, simple color swaps than overt costume changes.