Depends! Here is an objective snap shot: (BTW, I am assuming that you mean the SCT Programmer and not the "plain" one from SuperChips)
Diablo:
Can store one custom tune ONLY. Poor choice if you need multiple tunes say for n/a and nitrous or even an 87 octane and a 93 octane tune. Device offers some neat features that give the user some control over the tune and making changes. Things like gear swaps or when adding an o/r X pipe are simple with this device. Want to add a 180 degree thermostat, it is simple with this one. These changes can all be made by the user w/o mailing it in. Customer support can be hit or miss if you have problems. My experience was poor, but not the same as others. Most users I fear are ill trained and lack the knowledge to be making adjustments allowed by the device. I believe that Diablo realizes this, and make the adjustments that can be made VERY minor so as to not affect much anyway. Lastly, I have NEVER seen a serious racer use one of these so what does that tell you? Answer: I believe this device is marketed at the daily driver who wants to play with the car a little bit and wants some added power.
SCT:
Much better option for someone with plans to make major changes to their car. SCT dealers tend to be much more knowledgable and support is better. Device allows for three custom tunes. Great for a true street/strip car or one with nitrous. Tune changes can NOT be made by the user as the device needs to be mailed in for simple things such as changing gears. HOWEVER, with a $75 cable, tunes can be emailed. I have used this feature often. I think the tunes from SCT are better than those from Diable. Device costs more money especially if you want the cable and to pay for additional tunes.
Depends! Here is an objective snap shot: (BTW, I am assuming that you mean the SCT Programmer and not the "plain" one from SuperChips)
Diablo:
Can store one custom tune ONLY. Poor choice if you need multiple tunes say for n/a and nitrous or even an 87 octane and a 93 octane tune. Device offers some neat features that give the user some control over the tune and making changes. Things like gear swaps or when adding an o/r X pipe are simple with this device. Want to add a 180 degree thermostat, it is simple with this one. These changes can all be made by the user w/o mailing it in. Customer support can be hit or miss if you have problems. My experience was poor, but not the same as others. Most users I fear are ill trained and lack the knowledge to be making adjustments allowed by the device. I believe that Diablo realizes this, and make the adjustments that can be made VERY minor so as to not affect much anyway. Lastly, I have NEVER seen a serious racer use one of these so what does that tell you? Answer: I believe this device is marketed at the daily driver who wants to play with the car a little bit and wants some added power.
SCT:
Much better option for someone with plans to make major changes to their car. SCT dealers tend to be much more knowledgable and support is better. Device allows for three custom tunes. Great for a true street/strip car or one with nitrous. Tune changes can NOT be made by the user as the device needs to be mailed in for simple things such as changing gears. HOWEVER, with a $75 cable, tunes can be emailed. I have used this feature often. I think the tunes from SCT are better than those from Diable. Device costs more money especially if you want the cable and to pay for additional tunes.
I spent the last month comparing the Diablo Predator and the SCT Xcalibrator. Go HoTO! pretty much summed it up right here.
Diablo Predator: Good entry level programmer for someone who is just starting out. Learn and do it yourself. You can adjust and monitor certain parameters. It also functions as a fault code reader. When your demands increase (i.e., power adder) custom tunes can be purchased from a professional tuner and loaded via the Predator.
SCT Xcalibrator: Same as the Predator but you can't tweak stuff on your own right out of the box. No data logging or fault code reading either. It holds up to three tunes that you can easily load. SCT tuners take pride in their tunes and stand by them.
To even out the field....
Predator: There's talk already on the Diablo forums about a release that will hold more than one tune.
Xcalibrator: You can purchase a cable and software so you can do your own tweaks to the tunes, like the Predator. Or get the full up Pro Racers Package if you outgrow the amateur stuff.
Both programmers can be found on the web for $350.
Personally, I went with the Predator. I have a daily driver (auto trans) and my main goal was to firm up the shifts. I don't see myself slapping on a supercharger, turbo or nitrous in the near future. Not gonna race it. Not gonna rice it. When it came down to the final count, I decided I could use the Predator's data logging and code reading features more than the Xcalibrator's 3-tune storage. When it comes to the quality of the tune, it seems like SCT has the edge. However, my needs in a programmer are pretty basic at this point. Given my current entry-level situation, the winner is the Diablo Predator.