SM stands for Super Moto. That is, a dual sport or dirt bike with sport bike wheels and brakes. Because they run road tires, their off road capabilities are limited. The S is the standard street legal one (I believe) with standard dual sport tires.
The Yamaha WR-250 is also an option. The reviews for it are that it handles highways just fine, it very high tech, yet resilient, and plenty of fun. It also comes in both dual sport and Super Moto configurations.