Kyle,
I've got the Apex kit. I was pretty surprised at how frequently the Spax kits were apparently falling apart on owners cars. The reliability appears to be quite shocking (no pun intended).
Nothing but praise for my Apex kit. I've done 30k miles with it on now and not a single problem. Front is firm and the rear is very firm - giving very pointy, but precise steering. Seems to be a very well optimised setup for improved handling
The Spax springs on the other hand have progressive wound springs, meaning they start off soft and get progressively stiffer as force is applied to them - which basically results in sloppier handling.
Apex all over the Spax.