First thing I have to say is, Simms has really impressed me with the quality they provide.
Ok, after owning and fishing/wading with both of these boots, I'll go ahead and compare these from my point of view.
After owning Red Head boots (Bass Pro brand) for a while and having them fall apart completely on the stream (I mean the soles were floating down the river, etc.) I decided to step up to something better. I had owned a pair of Orvis Clearwaters years ago when I was an early teenager and wore the felt out but they stayed together. I was obviously in the market for new boots so I went with the Simms Blackfoot felt soles.
The Simms wins in comfort, ankle support, looks (which really doesn't matter), ruggedness and anything else I can think of except two categories. The Orvis are more packable and the felt is glued AND sewn on the soles. They were both the same price ($69.99) at Bass Pro Shops. BUT, I haven't worn the Simms enought to know whether I can go through the life of the felt without them falling apart like I did with the Orvis boots.
Simms:
http://www.basspro.com/webapp/wcs/stores/servlet/Product_10151_-1_10001_10205274_175009003_175000000_175009000_175-9-3Orvis:
http://www.basspro.com/webapp/wcs/stores/servlet/Product_10151_-1_10001_95996_175009003_175000000_175009000_175-9-3