Depends on what you mean by combat loss ratio. Kill to loss? Loss per sortie? Loss per 1,000 sorties?
Many people want things to look better than they are, so they do things like tout kill-to-loss for air-to-air only.
The F6F Hellcat was the best there at 19.1 : 1 kills per air-to-air loss. Some people say it is the FM, but the FM is a Wildcat. If you count all USN/USMC Wildcats, the air-to-air kill-to-loss ratio is 6.9 : 1.The Dauntless is 1.7 : 1.
However, if you count losses to AAA, Operational losses (ran out of fuel, engine failure, etc), the overall kill-to-loss ratio for the Hellcat is 4.4 : 1 (1,163 total combat losses against 5,163 combat victories) and it is the best. The F4U comes in at 2.8 : 1, the Wildcat at 3.3 : 1, and the SBD comes in at 0.4 : 1 or 2.5 combat losses per victory (341 combat losses against 138 total combat victories).
See my table below. Note the USAAF data is for the ETO only. The USN / USMC data is for the entire war. Also note you can find many different answers for the number of victories attributed to various aircraft. There is a completely different total at:
Warbirds and Airshows- WWII US Aircraft Victories. But, this website doesn't give you his source for the rather complete-looking table ... just shows the table.
At least my table below has sources shown even if it is not exactly complete.
View attachment 708971
Note: USAAC breaks out air and ground victories, but not air, A/A, and operational losses. US Navy data breaks out air, A/A, and operational losses, but not air and ground victories. To be fair, all combat losses are shown, all combat victories are shown including air and ground, and all combat sorties for US-made types shown. Excludes heavy and very heavy bombers.
Note: Many sources claim the F6F has a 19 : 1 kill ratio. The F6F had 270 combat losses to enemy aircraft, 553 to A/A, and 340 operational losses in combat. It shot down 1,445 bombers and 3,718 fighters for a total of 5,163 victories including both air and ground kills. If you divide 5,163 by 270 losses to enemy aircraft you get a ratio of 19 : 1, but the 5,163 includes ground kills and the 270 ignores A/A and combat operational losses. The numbers above include all combat kills and losses since the USAAC and US Navy do not break out their numbers in the same manner. This way, we compare apples to apples and get a fair ranking among US-made aircraft shown above. If more data surfaces, it will be added and compiled.