I have owned systems from all of these folks. Each system has its
unique advantages and disadvantages. They all work equally well, but
they all have a slightly different approach and perspective. Pick
which one suits your specific needs the best.
If you are drag racing or the like, I'd lean towards Derek.
If you need step-by-step installation instructions, Rich probably has
the easiest to follow instructions.
If you love all the bells and whistles, Davide' is a good match for you.