SCT: Pros: Most tuners use this type of tuner and tunes can be readily found for this type since it is so popular. The SCT is more specific to your car's computer. ie. They have certain serial codes of whatever one you get for a certain number of 3v computer codes. It is a good tuner for datalogging etc. and easy to use.
Cons: There is only one in my opinion anyways, and that is that it has a certain number of locks and unlocks. When you install a tune it locks the device to your car and your car only. When you restore the stock tune it unlocks it. Once that number is used up I believe you have to contact SCT and they add more?
Never got that far with mine and chances are neither would you.
Diablo: Pros: Pretty easy to use and also good datalogging capabilities. Almost the same as SCT. A couple parameters are different(don't know which)
Cons: Tuners for the Diablo are a little harder to find and makes it a tad more difficult if you have a problem etc.
In the end they really are technically the same. There are minor differences and such, but really all it boils down to is the tune that you are running.
So more on that. The 'canned' tunes in the device are ok for CAIs, but anything more than that, and even if you want to get the full potential of all of the mods you do put on your car, a custom tune is really where the power is at. Reputable tuners can either send you email tunes which you load into the device and then into your car. The email tunes are actually quite good and many times people have gone to get a dyno tune and when the tuner looks at the email tune they can't really get any more safe hp out of it. Maybe a couple hp. So for email tunes they are quite good and worth the 50-75$ that are charged. Good names are Bamachips, Brenspeed, Tillman, BBR, Brooksspeed, VMP etc.
Since you are close to Brenspeed I would highly reccommend them! They are a good tuner and when you buy from them they give a updated tune for free. So if you bought some LTs from them or cams they would update the tune you have for free. Other companies offer this as well. In the end it is up to you and what you want. You said low 12s so that means at a certain point you will need a dyno tune for sure! Also good datalogging capabilities. You could purchase the Trinity or the Livewire right now and have that for the future when you will need to keep track of parameters of your car, or you could just buy a handheld for now and purchase that later. Again up to you.
In my opinion and if I was in your place, I would purchase with the future in mind. A lot of people spend a lot of money on buying things twice. If you plan ahead then you won't or you will limit it a lot and save yourself time and money.
Good luck! Hopefully this helps a bit and there are more opinions than mine!