...interesting fight. I'm not exactly sure what Braniac is capable of. I know Ultron a lot more. As such, I would be rooting for Ultron, but from what little I do know, my gut says Braniac would probably win.
Ultron wins, he tanked an attack from a lot of powerful heroes and villains at the same time without any damage, he took over Phalanx, he took over Earth and was practically unkillable, Brainiac CAN´T win this.