Are you switching away from Kuiu? The reason I ask is because I've actually switched the opposite direction. Kuiu fit my long, skinny frame a lot better.
I don't have any experience with the Kuiu, but I have both of the Sitka, the Timberlines and the Mountain. They are basically the same pant, except the Timberline has the external waterproof knee pad and butt pad. Excellent performance if you are kneeling or sitting in damp conditions. The Mountain pant does not have the external waterproof knee and butt covering. They both have removable knee pads and suspenders.