The competition to get into certain specialties goes in cycles and changes in line with the profession. Endo used to be a relatively "easy" match. Right now it's hard as heck to get into. I would guess that in the future as more dentists are trained in implants and the costs come down, endo won't be such a hot specialty anymore. More and more people are just going to say "replace it" rather than worry about the hassle and risks of endo. At my school, an implant placement and restoration is actually cheaper than RCT/BU/Crown. Some of the faculty have told me they expect this to be the case in private practice in not too many years. Perio could get really hot if they end up capturing a major chunk of the implant placement market.
Pedo used to be a "walk-on" specialty, but is getting tougher every year. I think a lot of it is the tremendous increase in female dental students we have seen in the last several years. These gals have the same biological urges to bear and nurture children that every woman has, but many are pushing those urges aside to pursue their careers. Pedo let's them feel that they are at least getting in the "nurture" part. (I think that fulfills my politically incorrect quota for the evening.)
Prosth used to be a well-respected and sought after specialty. Now, with fewer patients needing that kind of extensive reconstruction and with new materials and techniques bringing those types of cases within the realm of general dentists prosth programs can't even find enough American grads to fill up their spots.
OMS is dealing with some of the same problems that our medical colleagues are struggling with - at least more so than other dentists. Add in a grueling 4 yr. residency and weekend call and there's no way it's ever going to make the very top of the list.
Everything changes my friend, everything but ortho.