As many have said before, many many many times, whats long-term and better suited is a matter of oppinion. Are we talking from a purely Special Events standpoint, a purely MA standpoint, or a mix of the two.
Ki-43
SE: important for PTO events only, needed, but of lower priority than the He-111 based on # of relevent events.
MA: needed for EW/MW, probably just a faster Brewster buffalo with even less armor in the LW arena, not very important.
He-111
SE: Imporant for EW ETO, Afrika, and EW-MW Eastern Front events, needed
MA: needed for EW/MW, Hanger queen in LW, not very important overall.
Panzer III (assuming multiple models are given):
SE: important for ETP, MTO, Eastern Front, between EW-MW. Needed above He-111 and Ki-43 based on # of relevent events (assuming GV's are used)
MA: Needed for EW/MW, hanger queen in LW.
From a purely MA perspective, none of the above are really important. From an SEA event, they are (within their own events). Mixed, it would probably be the He-111 or Panzer III simply because they can be used for a wider range of events, and give us something thats significantly different in the MA.