If you are not committed to Cherry mx brown switches, but you want great PBT keycaps on a premium keyboard, I can heartily recommend Realforce. However, I have their TKL boards (RF 87ub 55g and 45g). I have not tried their full-size boards. Their full-size with uniform 45g switches comes with high-profile caps, which I have never tried.
My other favorite boards are IBM buckling spring (Model F and Model M), which have great dye-sub PBT caps. These boards are plentiful on eBay.
If you must have mx browns, I have only owned TKL boards and cannot speak to the full-size models. However, in the TKL version, I have previously owned a Ducky Shine II, CM QFR Stealth, Filco MJ2 Ninja, and Kul ES-87. I thought the quality of the Ducky was not as good as the others, but I have heard that their quality control has gotten better recently. Costar stabilizers rattle a bit and make it somewhat tricky to install new keycaps on stabilized keys, but they are not as mushy as Cherry stabilizers.
I can vouch for the Leopold PBT keycaps. I have the Navy unprinted set, and they are of excellent quality for a reasonable price.
I also have some dye-sub PBT sets that I got from Imsto, geek_feng, and Ducky (eBay), but these are becoming more difficult to find and some of these sets fit rather loosely on the key stems.