The GTAC guys are generally all very good, especially the old timers, and I often see praise for them on the Enterasys "out-of-office" mailing list, but my vote for favourite goes to Alex Rotaru (even when he tells me to log a case). Who is your favourite?
In my 15 years experience as a customer, I can safely say that all the Enterasys GTAC people that I have come across are excellent and it is unfair to single out a favourite. But having said that, I remember that Alex makes damn good coffee, so guess that's worth a bit extra!!!