I bought the Bit of Britain unlined and liked it so much I went back for the lined version. My pony does not have especially prominent withers, but her paddock mate is a big TB mare with substantial withers and the Bit of Britain blanket fits her well.
The only problem we have withthem is that each weight comes in only one color, so you have to label your blanket well so you don't get it mixed up with others at the barn.
My old TB had the Schneider's New Briton line with the strap in the shoulders, and it fit him great. He also had high withers. The only issue I had was water getting on his shoulders, because if you end up tightening the strap, it creates a gap.
I will be getting my new TB (who has somewhat high withers) Schneider's for this winter, but the Euro-Fit with the comfort collar.