The 518 is an excellent mouse for the money. On my second one now,after many years of gaming. (Wore the old one out underneath).
I've dabbled with the Kone (Right button broke twice, so binned it), and the G5. The G5 is a good mouse, but doesnt feel quiet as comfortable in my big shovel like hands as the 518.
On a side note, I think a lot of the manufacturers must think everyone has the digits of a pixie. The button positions on some mouse designs are questionable, imo.