I have very wide feet, and the Simms Guide Boot is the most comfortable wading boot that I have ever owned. I have a pair that will be 3 years old next month with the Aqua Tread and Spikes, and they are in excellent shape.
The only complaint that I have is if they haven't been used in a week or longer, the suede on the outside gets very stiff. That disappears in a couple of minutes after they get back in the water. If I have a long walk to the river, I will soak them in water before I leave to go fishing. Simms reps recommend some type of leather softener, which I haven't been able to find.