During a recent conversation with a friend, we debated which martial arts provide the best base for MMA. I argued that the level and volume of talent and competition in a given discipline is often overlooked.
For example, if we compared Fighter A, an Olympic-level Taekwondo black belt from South Korea, with Fighter B, a regional Greco-Roman champion from India, I believe Fighter A has the "better" base for MMA. This is because he likely grew up in a more competitive and elitist environment, and is likely more talented and genetically gifted, as his odds of success were lower than Fighter B's.
The popularity of a sport plays a significant factor. Muay Thai, for instance, is more widely practiced and has more gyms, competitors, and events. While Sanda is also a great martial art, it may be more challenging to find a gym in your area, and even if you do, it may not be as well-equipped as a Muay Thai gym.