Actually, a better but not mentioned engine would have been the HeS 30/109-006, which would have had the advantage of more power and more development potential than the similar sized BMW 109-003 which had been originally proposed for the Horton, and for that matter, potentially far better than the larger and heavier Jumo 109-004. Unfortunately, the RLM didn't want it, as it was behind the other two engines in the development curve at that point in '42, and it languished as only some prototypes.
The Horton would have done best with a narrow axial flow jet, perhaps one of the early Westinghouse types, if we include post war sources? Any of the advanced 109-004s would have a bit more power, but would still have a poor power to size/weight ratio. There was the possiblity of an advanced 109-003 or follow-on design with better power to size/weight ratio, but they were still not much more than paper or lab hardware stage. The HeS 109-011 was a bust as an engine, difficult to build and possibly not as powerful as planned(?) and a bit fat for the Horton.
The engine-in-wing design of the Ho-IX apparently caused problems for swapping engines. The need to upgrade the powerplants as better engines become available is apparently the priamry reason for the engine layout adopted by the Gotha follow-on project "P.60"