GTB's have their issues as well.
The Spread Spektrum 6-cell versions have been releasing the magic smoke like crazy at the indoor track here while my XBR's have been bullet proof. The non Spektrum version of the GTB's have been plenty reliable as well.
Not sure if it was just a bad batch or what. Point is no matter what brand/make/model you look at, there will always be people who have had problems with them. No product is 100%.
Either choice is a good choice. XBR is cheaper and fine if you don't want to go below 8.5, GTB is good if you want something you can run any motor you want.
Just my $.02...keep the change