I just bought the 20, I couldn't convince myself that the extra $100 was worth it. I didn't see where the more accurate compass and altitude of the 30 was worth much for my type of riding (road, rail trail, etc). Perhaps mountain biking might have more applications where there aren't well defined roads/trails, and if you also plan to use the unit for hiking then I would definitely consider the 30. As for the ANT+ capabilities that would be nice, but honestly I ride for fun and not exercise, on the few rare occasions that I want heart rate info I'll wear my strap and watch thing that I use for the gym.