Whoever shoots first, I think.
I'd lean towards Balao, though. More chances of follow-up shots, heavier firepower up top, if needed, and of course I'll favor US Navy training above what was left of the Kriegsmarine at the time. I think most of their expertise got sunk in 1941. I may be wrong about this, but I think the Balao's radar and sonar were more advanced as well, increasing the chances of that first shot.
By the way, did you choose USS Becuna as your Balao picture consciously? I just had the good fortune to be able to tour that very boat recently. Vid's on youtube if anyone's interested.