which is better for gaming

Well... G1 sniper has by far the best sound chip ( on z87 market. NICs are pretty much the same but G1 sniper's Killer NIC has way better software which is amazing for configuring network/internet connection and prioritize the traffic the way you want.

Their build quality is pretty much similar. But if you want exact details G1 Sniper is better with its slightly better pwm and mosfets. Both use International Rectifier's 3563 pwm though. But Gigabyte using the newer "B" revision which has higher switching frequency.

All in all G1 sniper is better.