With the state of flux that brushless speed controllers are in, you may have a hard time in choosing one product over another. Like most things that you will buy for this hobby/sport it is important to see what is supported in your area.
Nothing will frustrate you more than to have a product that has features you don't understand how to use and no one can assist you because what you purchased is not used in your area.
I would recommend that you get a system that allows you to update the system via a computer such as the Tekin, Mamba, or KO types of systems. You will hear that the down side of these systems is that you have to drag a laptop/computer around with you to the track to use it's advanced features, however that is only partly true. You will need a computer to access the advanced features, it is not a requirement to drag it to the track with you.
You will also hear alot about the LRP SPX/SXX line of controllers and how easy it is to setup with the dynamic timing already built in to some if it's profiles. Again, this is true and does make it easy. The potential downside if you want to call it a downside is that they are early in the dynamic timing game, and you could possibly play the speed controller of the week if you are trying to keep up with the "fast guys".
Again, if you are thinking RCGT you may also be thinking about organized racing and your best bet is to see what others are running in your local area as they will ultimately be your best source of help/tuning when you run into issues or problems that cant be answered or explained on the forums.
Personally, I have the TEKIN system as they are the most active in updating their speed controller firmware and programming software to take advantage of new ideas, regardless of individual views on how they are updating the systems they are active in this area which means you are able to take advantage of the newest ideas sooner than with a speed controller that cant be updated. Good luck with whatever you buy.
†Tracks: SDAR San Diego Asphalt Racing/Discount Hobby Warehouse†
†Team HOLY Rollers† †www.socal-rc.com - Southern California R/C Forums†
†My Blog: http://majicmanracing.wordpress.com/†