I am a certified spinning instructor (STAR 3) with MDA. Although their program has lots of room for improvement (some--not all--of the CECs are stale and could use some revising) their organization is respected in the IDC community (but IMHO they lost some credibility when Johnny left). All in all, if you want to get certified to teach spinning, I would go through MDA. Reaction Cycling is taught for Bally Total Fitness. It's a Schwinn certification.