Evolution bipod. Which leg size?

None of them. I had a set and felt like they were going to break even with the collars. While i'm sure its not as much of an issue as it used to be I strongly feel that Atlas PSR is the better option. I had a Harris, then an Evo and was never quite happy with it for multiple reasons - 1) didn't feel as good to me as a Harris, the spring on the legs sucks, the tension adjustment while being very similar to a harris was easily broken (I broke 2 on barricades) and more. I then got an Atlas PSR and right out of the box I knew it was a better decision.