Athena: high Elemental damage and FR with maelstrom stacks, which also cause her to never consume Ammo or need to reload. Noteworthy that she’s harder to play as she needs to manage her stacks.
Nisha: Tombstone (kill skill) makes it so EVERYTHING can crit, including Rockets, flakker shots, etc, even when you don’t hit Crits. Super easy.
Distant Third: Claptrap has a skill called One Last Thing, which is basically a moneyshot that works on guns with splash and the flakker. Relatively easy, not nisha levels, though.
Jack and Aurelia are somewhat similar as they can do a lot of damage but a lot of it is reliant on hitting crits, but in general they’re not as easy or effective as the other three. Both also have high potential ridiculous stacking mechanics that are unwieldy to build up and are easy to lose.
Wilhelm doesn’t like bosses…he can do them, sure but he’s really, really slow, ESPECIALLY if he can’t Crit them.