I think it depends...there are many women on this board who relax every few months and their hair is long and thick. Then on the other hand there are women who press their hair every 2 weeks like pinkskates and, well, nuff said. So I think either way you can have long and healthy hair, it just would depend on how you take care of your hair after getting the relaxer (and the relaxing technique), and how you take care of your hair after the press (also the pressing technique).
Sorry if the answer is a bit vague, but this is really dependent on the person's hair and technique!