If you're going to be doing alot of piston flying I'd suggest an ANR set. They're not cheap, but what price comfort and protection of your hearing. I've flown with 3 or 4 full time instructors in the past year and they all had Bose ANRs, though not good for aeros.
I bought a Dave Clark 13.4 which, at the time, was one of the best passive sets available but I've found that it's not that compatible with many others sets. When I did my IR test I had to bin them as they weren't compatible with the Examiners - had to use one of his old sets which I think he'd worn in Ansons! Not an ideal start to my test.