The Army. The Army had more experience and more troops with experience making amphibious assaults, and both personnel were posted in both Pacific and European/North African theaters of operations.
The Marines Corps was entirely regulated in the Pacific, even though they had posted a few units in Europe, since it was part of the Navy. The Navy had its Pacific Fleet pummeled hard by the merciless bombing at Pearl Harbor by the Japanese, and was needed to mount a large offensive to recapture most of the islands the Japanese captured, which began the island hopping campaign. There were barely any islands in the Atlantic occupied by the Nazis, so there wasn't really a large Navy in Europe as much as it was in the Pacific. That said, the Navy played a large role in landing troops in Europe and Africa so without our navy, the army would have a hard time defeating the Nazis.
Air superiority by both Army Air Forces and Naval Aviators helped decimated enemy fighters in the air and gave our ground forces cover and advance through enemy lines after machine gunning and bombing enemy positions. It gave us the reason to mass-bomb industrial cities behind enemy lines (be it an enemy country or enemy-occupied friendly territory) to destroy the enemy's ability to wage war. It's the reason two atomic bombs were dropped on Japan that saved millions of Americans, Japanese, Chinese, Filipinos, Singaporeans, Koreans, Vietnamese, and Malaysians.