This depends on the model you’re considering. If you look at a newer model of both, you’ll be getting a carbon body with either bike. They also both feature full suspension for a general mountain bike. The main difference is that the Trek Fuel Ex 9.7 and the Top Fuel 9.7 are in the wheels, travel, and gear capabilities. The Top Fuel comes with either 27.5 or 29ers, while the Top Fuel Ex has 29ers and more gear capabilities. The Ex is better for a trail bike, while the Fuel could be argued for as an XC bike.