Better to get ASE certs working at a dealer or independent shop?

I've been offered positions at both a franchise dealership and a well-regarded independent shop. The pay is comparable, but I'm thinking long-term about becoming an ASE certified mechanic and reaching Master Technician status. The dealership offers OEM training and diagnostic tools; the indie shop exposes me to a wider range of makes and models.

My concern with the dealership is brand-deep specialization, which might actually hurt my scores on exams requiring broad knowledge. The indie shop is busier and I'd get more hours, but there's less formal mentorship. Since automotive service excellence exams cover all major systems regardless of brand, I wonder how much brand specialization at a dealer actually matters. The ASE practice test content is manufacturer-agnostic.

Has anyone navigated this decision? Which environment better prepared you for the ASE exams? I'm leaning toward the indie shop but don't want to miss OEM training opportunities that could help with L1 and L2 advanced certs down the line.