If I were to get one, I would get the RS over the GTS. My reasoning would be that 1, it is cheaper, and 2 they advertise that both will get 20% better MPG. I would like to know your thoughts about that.
I was looking into those a while back. I decided against getting any type of plug-in tuners because many people had said the power transition isn't as smooth, and also you should also get a DSG tune if you have a DSG/S-tronic transmission. So you'll need to buy both the race-chip and the DSG tune.
ECU tuners are smoother, but the DSG still needs tuned from what I remember.