Almost certainly the Ki-84-I-Ko with two 20mm Ho-5 cannon in the wings (150rpg) and two 12.7mm Ho-103 machine guns in the cowl (350rpg). Of the 3,514 Ki-84s built about 200 were pre-production aircraft, 2,800 or so were Ki-84-I-Ko as I described and about 500 were Ki-84-I-Otsu with four 20mm Ho-5 cannon, two in the wings and two in the cowl (150rpg).
Less than 10 Ki-84s were armed with two 20mm and two 30mm cannon, but in IL-2:FB that version is insanely leathal. It is not clear that it every saw combat. It is almost impossible to shoot down the B-17 or the big German six engined transport with the Ki-84-I-Ko or Ki-84-I-Otsu in IL-2:FB, but the Ki-84 with the two 30mm can blow either into little bits with hardly any effort at all.
What I wouldn't mind seeing in AH is the Ki-84-I-Ko as a free aircraft and the Ki-84-I-Otsu as a lightly perked aircraft in the same vein as the F4U-1C. I do not think the 30mm armed Ki-84 has any place in AH.