A first horse will be a teacher. Therefore the first horse should know more than the student. Breed is less important than temperament and experience in the horse.
That said, I don't favor gaited horses as first horses. A trotter teaches better balance and appreciation of equine movement. It permits the free application of training in a very wide variety of philosophies where adding gaited movements can muddy the instruction.
After a couple of years learning basics the rider can easily shift over to a gaited horse and then progress building on their foundation.
P.S. And the quality and competance of the instructor for the first time owner is also much more important than the type of horse involved.