CsC
The P&Ws in our current aircraft are excellent engines and very reliable.
As to comparative stats, someone else will have to give you those ( and I can guess where you're going with the current line of enquiry
), remember there are lies, damn lies and statistics.
Frequency of engine failures:
During the short time I flew gazellicopters I can't recall a single engine failure occurring in the fleet. (that doesn't mean there weren't any, but I can't remember any!). However, during the equally short time I flew 355s I can recall a number of pilot induce engine shutdowns due to engine chip warnings. Now from that you can work out a number of things
astazous are better than alison/RR250s
the 355 should have been powered by astazous
singles suffer less engine failures than twins
my memory is s**t..
If I had to auto anything I would rather it was a bell 47 or a huey
(and I've flown neither). The fact is, that if your only method of propulsion fails over a built up area you are better off in an airship! (with a very small leak, and light winds, and a long rope ladder).