I have used all 3 before and I gotta say, you wont be wrong with any of them
If you are on stock turbo, power and torque would be basically the same (give or take error compensation from a lot of variables and ambient variations) with either of them given they use the same fuel quality (91,93 or e30).
Between the 3 that you have listed, Stratified and Dizzy offer a "canned" flash tune and also custom tuning , JST only offers custom tuning
My opinion of them:
Stratified:
What I like: is a really good base flash tune, hardly any neg correction, pretty much dial in for the fuel you are using.
What I don't like: customer service over the year has become terrible, a flash tune takes up to 5 days ( last time I had one, ver 3.9ish, I don't want to imagine now with the volume of the new version),
Some basic features that should be free "cost money"
1 datalog review cost as much as the tune itself
Dizzy:
What I like: customer service, you can shoot him a message here, on facebook on his personal facebook or his business one or his email and he will respond you quickly. He has some cool investigation testings like the intake comparo dyno running he did, etc.
Also a really good base flash tune, hardly any neg correction, pretty much dial in for the fuel you are using. It cost $75 ($25 more than stratified) but includes a free datalog with it
Basic features can be change at no extra charge
Quick turnaround, 1 or 2 business days for the flash tune
Free decal swag
(This is my opinion) I like more his tuning strategy over the others. If you compare all of the 3 tuners, (93 oct) You can see he runs less max boost, 24 psi to 26 psi of the others but compensates with timing (since all 3 are pretty much the same as term of power/torque) but if you see ETC angle on a pull, dizzy never drops from 82 etc angle compared to the others, that etc angle just plummets to control boost. In other words, the tune is very optimize for the car/turbo. Again, This is my opinion of how I understand the tuning strategy for our platform, you are welcome to tell me I am wrong If I am, willing to learn here.
What I don't like: I have been thinking but I cant seem to find anything I don't like, He know his stuff and is a pleasure doing business with him. I guess not having a lifetime tuning? IDK
JST
What I like: Just like Dizzy, customer service is on point, you can email him or message him on facebook and is quick to respond
Free decal swag
Quick turnaround
He knows his stuff for the platform and since this is a custom tune to your vehicle, Is gonna be good for the fuel and your driving style, given you give him the feedback he needs (You know, nitpicking stuff like what should idle rpm be, throttle curve, Cobb TC enable or disable by default, etc etc).
He offers a lifetime tune if you want that but in my opinion, Tune+ offers a better lifetime tuning option for the money
What I don't like: He doesn't have a flash tune option, so people could have a taste of what he is capable of. You expect a good tuning calibration because of the good feedback he has receive from the FOST guys, facebook pages and such, but other than that, you don't know what he is capable of, unless you fork $150, since that is the price of the custom tuning.
You cant go wrong with any of the 3 since power and torque is gonna be pretty much the same on all 3 on the stock snail ( the turbo is the limiting factor, not the tune)
If I where in your shooes I go with a flash tune from dizzy just to test the waters. Awesome costumer service, quick turnaround, you can change basic options (like idle rpm, If you want Cobb traction control enable by default and what number to set it, LC default RPM) for free, free decal swag.
If you want a custom tuning (don't expect something absurd like +20hp and +50torque compared to a flash tune because you wont see it, it is more a tune for your car, your fuel and your needs), if you go dizzy or jst you wont be wrong with either of them. Same price, same custom ability for settings or nitpicking that you want. The only difference is the their tuning strategy (what I said in the what I like about dizzy), but other than that, both are awesome.