I've had all of the above listed and my favorites: Sitka Gaitors. Sitka doesn't get much "play" when it comes to Gaitors, but they are my favorites followed by OR, and KUIU. The Kenetreks I had did not last.
I've had my Kenetreks for the past 3 years and really like them. I have the RealTree camo style and they have kept me dry and they are quiet as well. I hunted with a guy this year that had the black OR gators and they made noise with every step he took.
Expedition Crocs, lose the under boot strap right away and tie some cord in. The buckle always gets wasted and it's much easier to field swap some cord.
Kotaman is right. Sitka gaiters don't get recommended much. I think its because of the price.
I have a pair of OR exped crocs and think that if you are going to be wearing crampons, these are the best.
I have a pair of KUIU gaiters and think that if you want slim fitting, brush and snow gaiters, without crampons, these are best.
I also have the Sitka gaiters. If you want the best all around gaiter and most comfortable to wear, these are best.
All are waterproof. Well, kind of. The sitka and the OR are goretex so that means "semi water resistant" not actually waterproof.
But they advertise them as waterproof gaiters anyways.
My Sitka Stormfront gaiters are tight and don't fit all pant/boot combinations plus they make noise if you accidentally rub em together while stalking. Looking for a quieter and more flexible gaiter.