i have never tried a razer, but i have a G5 and an MX518.
the only thing i do not like on them is the mouse wheel. the G5 is too high up and the MX518 is too low, they need to put them right in between! also i try not to use the MX518 mousewheel too often because i have this weird feeling that it will come loose and lose its "click" feeling, if that makes sense. it just feels a little fragile. i like how on the G5 you can click the wheel left or right, its annoying at first but you get used to it in a few days. i like how the MX518 has two thumb buttons. the G5 has a really good cord i am sure it will never break. oh and sometimes the G5 right click kinda wigs out, i dont know why.
the drivers for the mice are really good they allow for a lot of customization.