So the Scott and the B3 are basically the same release. I have heard that it can be hard to find the Sigma at times. Alot of killers seem to use the Wise Choice as well. All three are amazing choices that utilize top of the line sear systems. I would say how the release fits in your hand, and how it affects your draw length would be the determining factors.
I have a wise choice. I think it fits great in my hands, which are on average smaller than most. If you have big ol meat claws, you will want to try before you buy. The release is crisp, but I enjoy the Stan shootoff and Chocolate lite more than the WC. If it is your first thumb button, I think you'll be satisfied. If you've been shooting Stans, you might be underwhelmed.