I wouldnt say SCT is the best, I have both Diablo and SCT and they both do the same job , you need to be looking at the tuners as well as the devise that loads the tune
Diablo only offers a flasher for the SVT Focus so your back to the SCT and for 379.00 you get a lot for the money if bought through me , you get
A XCAL3 that can load the custom tune to your car
Life time free NA tunes as you mod
The ability to read and clear Check Enging Light = CEL
A scan tool to check about everything that the engine is doing in real time
And more
Tom