When Merrill vaulted in the 1970s, you found a surcingle any way you could get it and it wasn't easy. When she vaulted in the mid-1980s with Kitchy's team, you still couldn't buy a surcingle in a store anywhere in the USA. You had to know somebody who knew somebody who would bring one to a competition in Europe for you - and in those days we rarely vaulted overseas. You had no choice in what you were getting and (usually) took it, thankfully.
Now, there is such a variety - which means choice! Of these many surcingles, which is the one best suited for your needs?
Below is a link to an article, written by Megan Benjamin, in the American Vaulting Association, with updates added by ourselves, and also informal advice based on experiences and feedback.

Equestrian Vaulting Magazine Vol. 45, #2

Our thoughts on the subject:
First, competition vaulting is a vigorous and demanding sport, requiring a surcingle built for its rigors and demands. We recommend a Meinecke competition surcingle. Far and away the most popular selling competition surcingle is presently the Meinecke LD. These handles allow for more creativity, security and difficult exercises than the old standard round grip surcingle. We also offer additional competition surcingles with differently configured handles for the competitive vaulter. Read their descriptions to see which might suit your needs (i.e. the Kristina has higher and wider grips that suits men well, but not smaller vaulters).
Non-competition - and beginning competition - vaulting is a different matter. Beginning vaulting clubs, camps, riding programs, therapeutic uses and recreational vaulting groups often have the option of using a less expensive surcingle imported from India. The PE surcingle works well for such vaulting uses. The PB slender and Meinecke Therapeutic surcingles are useful for improving harmony with the horse and modified vaulting - especially for children who are working on placement and balance on the horse (therapeutic and riding clubs), as these surcingles are thinner and allow shorter legs more proper placement. The Meinecke Therapeutic surcingle is a high quality surcingle custom-designed by two therapeutic vaulting instructors to specifically address the needs of therapeutic vaulters. These two surcingles are not designed for flight or other rigorous vaulting exercises.
Keep in mind, that if you have competition in your sites, you might be best buying a competition surcingle from the get-go. Everyone gets used to it, and it's an expense that is coming anyway. On the other hand, some clubs need an inexpensive surcingle to get started, and then build into the competition quality. What is best in your situation?
We hope this has helped.
Best of luck with your vaulting program!
Pegasus Vaulting Supply