I think the B18C5 and B16B were both EXCELLENT for what they were made to do. From what i know of the SR it's awesome as well, same with the 3S.

I think this question is a bit too broad though, different engines do different things. You can't compare the ITR to the SR when speaking of brute power, one will far surpass, as you can't compare the two for road race, at least not to my knowledge. So are we looking at power, how fun they are to drive, road racing criteria, or longevity?

Ps. The 4G can suck my dick.