Actually I have broken down the differences between the unit before!!
Here it is in a nutshell.
Diablo:
- built in datalogger
- about 400.00 (I dont remember the exact price)
- 1 tune per box
- pretty interface
- can accept tunes via mail
- no self tuning option (that I am aware of)
SCT:
- No Datalogger (currently)
- Up to 3 tunes on 1 box
- 325 dollars
- No digital display
- Upgradeable to the Pro-Racer self tuning package SCT Pro Racer
- Extreme Tuner (I forget the name actualy) allows tunes by email with the EU able to make small adjustments (I believe this is accurate, I cant find the thread)
That's the hardware.
The most important thing is go with a tuner you trust, and thinking long term, go with whatever is supported in yoru local area. For example hypnotic, focusSport, Tom etc... will all be able to work with you via mail for small NA changes. But if you ever decide to go hardcore and go with cams or FI or something, than tuning is an issue and you might want to go with the package a local tuner is familiar with.
Or also think ahead about what mods you want. If you plan on using the FS cams at some point, you will definately want the SCT flasher, as they are the ones who will have the tune for it. If your going to go with Turbo Toms Turbo kit, well you want the diablo...
Hope that helps!