Never been in a piston powered Helo and never intend to!
Now turbines ...... my opinion the CT7/T700 leaves everything else for dead exellent power to weight, good fuel burn and reliable (forget obout the couple of problems in the S-92) , fitted to more Helos than any other , S-70 series,AH-1 Cobra,AH-64,EH-101,S-92,Retro fit to B205/UH-1,B214-ST,YUH-61 , SH-2-G, etc, How many thousand helos is that.
Have worked on A/RR 250 series, T-53 ,T-55 ,CT/T58 ,Makila ,Arriel ,PT6T Twin Pac, and none of them come close.