Voted for Beetle, Aqualad, and Miss Martian.
They all have history with the cartoon version, so there's a nice balance between the comics' YJ4 and some of the major players from the show. They have great, varied skills and abilities. And it doesn't hurt that it also improves the representation factor with another woman and two men of color (one of whom is also gay).
I also voted for Ravager and Artemis because I voted before noticing that I was supposed to limit it to three. My bad!
I think the book could handle a roster of nine though. And Artemis and Rose bring some nice dynamics and abilities with them.