"I noticed on the TUF series, they use Aerodyne bikes. Then when watching "UFC: All Access - Sherk", he has an Aerodyne as well."
Best bike for MMA Training would be the Air Bike Stamina® Airgometer Exercise Bike
The Stamina® Airgometer Exercise Bike is quiet, smooth, and reliable to withstand seriously intense workouts. This air resistance bike is simple to use yet comfortable with the wider, cushioned seat, weighted, textured pedals, and padded dual action handlebars.
Cycling improves your cardiovascular fitness and strengthens your entire body including legs, thighs, hips, calves, arms, and chest. The dual action handlebars add an upper body workout and more intensity to your workout to burn calories and fat.