Probably Matsuri or Subaru, they really deliver the complete package on stage. Extremely high energy, good dancing, good singing, they're very strong.
Nene is also obviously great at this, but so far she's been nerfed by her musical taste, imo. Hopefully they get her to perform Make Up True at 3rd Fes, that's the best original she has, by far.
Aqua, Suisei, Flare, Sora, Roboco, Aki and Towa are also great choices.
I want to say Marine qualifies as well, but since she's my oshi I'm obviously biased.