Man, I don't have a switch yet. But if I did, I'd go for the new Smash first. Mains for me include:
Mario, Dr. Mario (or Melee Mario now), Luigi, Bowser, Pac-Man (aww yeah, son), and Princess Peach
And for Side Knights/Wild Cards include Sonic, Donkey Kong, Diddy Kong, Toon Link, Link, Young Link, and Captain Falcon!