Hughes 500:
I too would prefer a B over an R, but in America, the market seems to like R's as it does pay more for equivalent ships with an R over a B. Most users think, oh another 25 SHP.........
Personally, I prefer a C30 in mine.
Like most engines, you make more power by pushing more air more efficiently through the contraption. B's are simply less stressed and as such are more reliable and more likely to make it to hot section and overhaul without intermittent repairs. Rolls would disagree but I think the field experience data would support my observation.