Gunslinger is one of the best subclasses for Rumble. Since you’re primarily going to see enemies one or two at a time, it’ll be easy to clean them up with your super and move on.
Also, Rumble has the unique setup where all five other players are your enemies. You can take advantage of your fast-twitch skills and pull the trigger the moment you see another Guardian rather than picking friends from foes.
Sunbreaker can also break multiple skulls, given that you opt for the perk that returns health when you get a kill with your super hammers. One of the important things to remember with this subclass in Rumble is to start your super before a fight, not during it. The charging time is long enough that a crossfire will kill you before you can sling a single fiery tool at anyone.