I used to use the Alpha with earplugs jammed in. Good noise reduction, but the helmet gets very hot and sweaty, and earplugs tend to make my ear canal ache after a while.
Now I use the Bose X. In fact, I just did almost 8 hours in a Puma without a a niggle or pain anywhere. They are very light and very comfortable, and the sound quality is superb. Makes a big difference when trying to decifer HF transmissions.
The only drawback is the very flimsy battery pack. For applications where you need to wear a headset outside the aircraft (i.e offshore) it can be a pain in the @rse finding the right spot to put the battery pack without it getting knocked off.