As in most purebred animals, there are some genetic problems that creep in from time to time, but responsible breeders work very hard at keeping their lines as healthy as possible. Things to watch for in any cat, purebred or not, include umbilical hernias, heart murmurs, and kidney disease. In size, they are about what you think of when you think of an average-sized generic cat. This list includes many breeders who are ethical and offer healthy, purebred kittens. To be honest, the main difference is largely individual preference.
Some people adore the new look, while others hate it.
As far as personalities go, in general, Traditional Siamese tend to be a bit more laid-back than their modern counterparts. But individuals will vary, and you will find very lively Traditionals and mellow moderns. Either type can be a delightful pet. As such, they are unable to compete with modern Siamese cats. Though theoretically there is nothing in the show rules that prohibits a registered cat from competing in its breed class, in practice, very few people attempt to show them as Siamese.