I love my ASUS X99-Pro. My previous board was an ASUS Z97 board, which was great as well.
On an unrelated note, I still miss my old Abit KT7A-RAID. ::weep::
I have an X99-pro/USB3.1 as well and I'll echo this sentiment. I like the board a lot. Aside from a problem flashing the BIOS which has nothing to do with the board itself but with lack of documentation and partly a very small error on my part once I figured it out, everything else went smoothly.
Delivers as promised a smooth cpu overclock and everything works as advertised on it.