You really won't find a board 'better' for gaming or not. If they support SLi or CrossFireX, they're about as 'gaming' of a motherboard as you'll get. Now, if you're looking at overclocking then it may matter but, not between those boards.
However, the UD3P appears to be PCIe 3.0 compatible so that's the one that will allow better graphics upgrading opportunities in the coming year or so.
They both look like pretty darn good boards. I primarily use Asus boards so you'll want to look at the reviews of the board but, Gigabyte is my second choice for consumer desktop builds so, it should make a darn good setup.
edit: If I'm looking for a 'gaming' consumer machine though, a higher -end full-size ATX board with 2 or more PCI x16 slots AND a couple x1's. Also make sure that the MOSFET and Northbridge/Chipset have nice coolers or heatsinks. And more, if you are looking to go to the next step, check replacement cooler options (waterblock).