I have every Spinerval except No Slackers and the one Coach Troy released this week. Without a doubt, doing Spinervals has made me stronger and has improved my cardiovascular fitness. Doing Spinervals is what got me back to riding outside again, so I am indebted to Coach Troy. I love riding my bike outside My favorite Spinervals are Uphill Grind (tough but relatively short in duration); Have Mercy (if you don't want to do the entire 2 hrs, you can pick & choose sections); all three Aero Base Builders ("blue zone" workouts); and Time Trial Special (has one leg drills). The least favorites are Muscle Endurance (it has 2 sets of acceleration drills that I hate--4 seconds on/4 seconds off) and Bending Crank Arms (too much off the bike ISO squat work).