I've trained with Clint Smith on several occasions.
He focuses heavily on fundamentals, and does an excellent job teaching the importance of laying a solid foundation for skill. His instruction is a bit dogmatic, and I've found that I've evolved in my own training beyond the point where I find Thunder Ranch to be the best use of my training time, but Clint is an excellent instructor, and certainly a "can't go wrong" training opportunity. For those who find Oregon to be out of reach geographically, Clint also teaches occasionally at Tiger McKee's Shootrite Academy in Alabama, and Tiger is one of Clint's disciples so to speak, having a very similar teaching style and set of instruction.
Never trained with Mas Ayoob, so no opinion there.