I know many soldiers did not have a choice because they were drafted into whatever branch needed bodies, but did soldiers who enlisted normally lean towards the army because they would most likely get sent to western Europe or the Marines or Navy because they would most likely get sent to the Pacific?
The 2/1st battalion of the 6th division Australia fought in both North Africa, Crete and Kokoda in the South Pacific. Veterans of both have said that the pacific was far worse. They suffered greatly in the hot humid conditions. With the large amount of rain malaria and dysentery were common. The other thing was in such thick jungle and tiny paths seeing more then a couple of metres in front of you was next to impossible.To give an idea of the conditions here is a photo of the track.
https://www.awm.gov.au/collection/026852/. Source australia goes to war 1939 to 1945 by Robertson J.
From my understanding U.S. GI's much preferred fighting in Europe to the pacific front. A major reason being the Japanese rarely surrendered. The Japanese also did not adhere to any standards of war, often targeting medics and casualty depots. It was perceived that the Japanese were fanatics and this caused a worrying sentiment in the allied pacific front.
The Japanese, according to the Bushido code, viewed surrender as dishonorable. Therefore they treated anyone who surrendered to them as dishonorable (see Bataan Death March). The Germans were more likely (but not always) to take prisoners and treat them more respectably.