I'm using G600 for all my abilities. For reference, it has a 12-button numpad for your thumb, perfect for a hotbar. I have no trouble hitting any of the buttons on the mouse so I just use them for everything.

Hotbar1: 1234567890+- (generally all GCD combos and abilities)
Hotbar2: alt+1234567890+- (offensive cooldowns, jumps and such)
Hotbar3: shift+1234567890+- (defensive cooldowns, call macros, items)

Mouse is basically bound to a number bar and I use modifiers from the keyboard like alt, shift, ctrl for other hotbars.