It seems clear to me that the choice of theatre depends on what one would hope to accomplish.
If I were seeking glory (assuming I would survive the conflict), as a citizen of the USA I would select Normandy, or maybe Bastogne.
If I were seeking to help enact victory (assuming my presence could somehow do this such), probably I would choose one of the turning points of the war. The naval battle of Midway or Guadalcanal would be tempting…but I under this assumption I would choose the battle of Wake Island because it was possible for a US victory. Had this happened, a naval turning point 6 months earlier than the battle of Midway, I presume the Pacific war could have ended 6 month sooner…though of course the necessary surrender of Japan might still have required the A-bomb.
If I were seeking to survive the war, I would definitely want something like the US coast guard defending the Panama canal. Nice and quiet with no casualties.