This is how all the various sources of DK3 difficulty settings compare to the original manual. The manual itself does not list any factory defaults or recommended settings. In my opinion, discussion regarding DK3 difficulty should use the terminology set out in the original manual. So, the Trifecta settings listed below use that terminology. If there is any confusion, people can come back to this post for reference.
DK3 Manual MAME TG Arcade TG MAME RU Score Mode (based on MAME 0.135) Easy (1)<------>Easy<--------------------------------------->Easy
(2)<------>Medium<--------------------->Medium
(3)<------>Hard<------->Medium [3]
Hard (4)<------>Hardest The current requirements for the Trifecta badge are:
1. 1,000,000 on Donkey Kong [3 lives, extra life at 7000]
2. 1,000,000 on Donkey Kong Junior [3 lives, extra life at 10000]
3. 1,000,000 on Donkey Kong 3 [3 lives, extra life at 30000, additional extras every 30000, difficulty 3]