From the look of the ingredients, I'd say that there's not really much between the 3 of them really. Wainwrights and JWB are about the same re protein levels, Burns is lower (that's one of their "things"). But all 3 appear good brands (haven't really looked in Wainwrights, but the ingredients look good). I think that Wainwrights is Pets At Home's own brand, which in itself makes me a bit leery, but hey that may just be me. I wonder who makes it for them?
Out of the 3, only Burns don't test their products on animals, if that makes any difference to you!
Are those the only 3 you want to consider, and are there any particular factors that are important for you?