The difference between these two can be seen on Ofna's homepage.

I have the lx pro and it has taken some serious beating! The only things broken are a spur gear (plastic) and a brake disc!
Other than that I damaged the standard servo when I hit a rock that was bigger than the buggy with nearly full speed. But that was a good excuse to get a better servo.

I've bought a lx comp, but haven't tried it yet since it came without engine and radio.