I'm a filthy casul who doesn't even Pokemon Showdown. I just know these builds because I built them for fun on my games, I never really fought other players. Contrary sweeper Serperior is risky, but also easier, since it kind of sets itself up to sweep. It's risky since it puts itself out there, but it's easier because the directive to have it set to sweep is very simple.

There's also for Rayquaza, that canonically, no one except for the main character in ORAS can Mega Evolve Rayquaza anyways, even in that game that shit required some special stuff to occur.

I may choose Gallade for my Mega though.