I used felt for a long time, but found that in the winter in ice/snow, or anytime in mud/muck they were more dangerous than good when I was walking the bank, or walking in or out of a stream. I do a fair bit of hiking to fish, so I needed boots that were not just good in the water - but also on land.
I have found that good rubber, with good studs is the best combo. The newer vibram soles are very grippy. Orvis posigrip are my favorite studs, with the patagonia/gripstuds brand second. Carbide studs are a must, as tungsten carbide is both rustproof and much harder than steel. I have not tried the aluminum foot tractor bar types, but can not imagine how they would be better.
My only gripe with grip is stud removal/install becomes an effort without a powertool. A small battery operated driver makes this easy. Also, stepping on flyline/mono with studded boots, or heavily lugged rubber boots makes for an annoying time.