I like the Zboard Merc because the gaming pad on the left side. The software has lots of profiles for different games which can be changed on the fly. You can also customize the profiles (I added a vent key). Zboard also adds profiles as new games are release. The keyboard only cost $40.00 at Best Buy as compared to the G15 which is around $100.00. The Merc keyboard is better for FPS while the G15 is better for games like WOW where macros are used (just my opinion).
Hope this helps you out.
Hope this helps you out.