Re: durability felt vs rubber?
I am with Fly2Fish.
I have a pair of Cablea's felts that I screwed the Chota cleats into and they worked great for my fall/winter wader fishing. ($6 for 28 cleats, 14 per boot)
I also have a pair of Kokers with the interchangable soles for my summer wet wading. I've got all the soles and for traction you really can't beat cleated felt. The next best if you are worried about micro-org-transfer is the cleated rubber soles.
If you do a lot of walking to get to that spot... get a pair of Korkers. Start out with the rubber only sole and switch to the cleated sole when you get to your spot. Switch back on the way out.
The key is to make sure the interior bottoms (Boot ans Sole) are clean and free of stuff. You don't even have to take your boots off. Just the sole!