I suppose the logical choice would be Broly, but that's outlandish. I'd like to see Kale and Caulifla join, they're a couple of badass Saiyans the team could use, and who wouldn't want to see more of Kefla kicking ass?!
If you could pull one character from any realm (cartoon character, sitcom character, anime character, etc.) and throw them in the DB universe, who do you pick?