It all depends on what you want.
My S3 has been chipped by MTM via Kim Collins. I did not get the car done, it was done by the previous owner (saved me a packet /ubbthreads/images/graemlins/grin.gif) so I cannot comment on the customer service they provide. I havnt heard of any bad reports though.
I dont have the Miltek exhaust either, but have a Magnex cat back, which I think is virtually the same.
I can however comment on the performance of the car. It is exactly what I want, and suits my driving style. There is loads of low end torque, which is what I like as I dont have to rev the nuts of it all the time. (Although its still hard not to. /ubbthreads/images/graemlins/devil.gif)
I have read on here countless times that "the MTM chip tails off as it reaches the redline," To be honest though I cant say I've really noticed. You do get a sudden urgency when you nail the throttle as I've said which smoothes out, but I wouldnt say it runs out of puff, if you get what I'm saying.
At the RR day at Well Lane that a few of us from here attended it produced 269bhp as quoted by Kim.
Heres the dyno plot
Theres also videos here of the day here
Rolling Road Day Vids
The ones of mine are labelled rr_s3_blue.#.#
I'd definately say DRIVE before you decide on any upgrade.
You could always come to the Christmas meet at AMD and I'll take you for a spin. There will also be other people with different tuners remaps/chips fitted, and I'm sure if you ask them nicely they'll oblige.
What ever you decide - Enjoy /ubbthreads/images/graemlins/beerchug.gif