I am now going with MyTailor shirts exclusively. I took measurements off my best fitting shirt and built my own measurement template online, including specifications for the armscye. I have a pretty normal build (right shoulder just slightly lower than left), so I didn't worry about below to accommodate it. I would guess my fit could be improved slightly if I got feedback from Joe, but I don't want to take the time or risk. I ask for unfused medium collars in the wide British spread and they are perfect for me -- soft enough but look sharp with a tie. I have gone mostly with Mason, Alumno, and Monti Prince Rose. But honestly the executive collection fabrics are very good and maybe the best deal on the site. Oh, and specify thick MOP buttons in your order -- they are high quality.
By the way, they do cut a good deal of shrinkage into the shirts, so I typically soak and throw them in a medium heat dryer the first time I pull it out of the box (rather than having to wait several hang dries for the shrinkage to kick in). If the shirts seem to big out of the box, that definitely is by design.