I say playing a lower tier character at this stage in the game might give you an element of surprise so make sure you're always looking for broken stuff specific to that character. You will know the meta / snake matchup better than they will know yours so thats pretty much the only benefit you're going to have going in playing against them. It looks like the only REAL bad matchup for jiggly is Game and Watch. You wont be able to keep the element of surprise for long (if you can even anymore). There's nothing to jiggly that I don't think everyone and their mother knows though. You're going to have to be a better player than your opponent and that's that.
When I'm dealing with top tier players, the last thing I want is a disadvantage on them. Go in with the mindset that you basically can beat everyone. Personally, I don't like the idea of having more than 1 other side character for competitive play but thats up to you. Marth is not a good choice vs snake and metaknight. You have to KNOW marth for it to be an even matchup. People with projectiles give snake a problem (like ROB). Snake gives Metaknight issues as well as Marth.
Rob isn't that hard to pick up. Neither is snake. I'd make your secondary somebody not too hard just for having a little edge on the matchup. I'd second snake if I were you but look into it. Snake's pretty easy to pick up too, imo. He takes some creativity to play, but as far as control goes, he's not that hard. Learn your dash->usmash cancel, how to drop/throw grenades, and how to ftilt (takes a little practice at first if you're not used to it).