I have tried almost everyone and so far I think that the Chahin leather from American Leather Direct is the best option. The thicknesses are accurate and the back on all the leather, split or not, are pasted. Yes there is some inconsistency but for me it's not been enough to make a difference. If you ask for a split, as opposed to buying already split and pasted, you are going to be subject to the vagaries of whomever is doing the splitting and will probably get no pasting.
I think the backside of leather work is important. I don't want crappy looking stitches and I don't want fuzzy looking split leather that I have to paste myself.