I fly with both an Alpha Mk10B and a Gentex HGU-55/P, and way prefer the Alpha. It's a little bulkier, and awkward to get on, but once on, it feels light, has a better visor arrangement, is more comfortable and has better earpiece pressure. In defence of the HGU, it does not have a custom fit liner, which would have been moulded for my head (but then neither has the Alpha).
That's just my preference, of course. Hope it helps.