What engine would you all consider is the most versatile? That is, it can be used in diferent type sizes/style planes?

Of course everyone has a 2 cycle 46 in the hangar, but what else are you finding is a super versatile engine that will fit in a lot of stuff? Maybe a 90 size 4 stroke? I see those go in just about anything including 40 sized 3d'ers.

I am looking for a 4th plane (looking at possibly a sig bipe) and already have 2 46 2 strokes and a 40 2 stroke and was wanting to broaden my engine collection. Wanting something that can be versatile for various planes.