they're on par. it's like if I give you a million dollars, what's better - in cash, as a check or trasnferred to your bank account -- it's all the same in the end with some conveniences
ASUS comes with a nice and easy to use BIOS. it's very nice to look at and to find things while GIGABYTE's BIOS is less clearly arranged.
the Gaming 3 comes with a KILLER LAN chip that let's you proritize the data usage of your applications.
the UD3 comes with 12 power phases and should therefore distribute power cleaner, go easier on the curcuitry and let you reach higher overclocks than the Pro Gaming (10 phases) and the Gaming 3 (7 phases). if you will recognize a difference, I'm not so sure.
Asus adds it's SupremeFx software to the Audio chip which is supposed to boost the sound experience, but honestly it's mostly marketing
the Gaming 5 would be a step up from any of those but is probably overkill for you if it's more expensive.
you can gladly get what you can get at the lowest price and what looks nicest to you