Having gone to one of the schools that does not have class rank, this is what I can tell you with a good degree of certainty. The ones that I am aware of are Columbia, Harvard, and UCLA, and maybe UConn (there may be others, but I'm not sure). When I graduated several years back, A LOT of people placed into specialty programs. Pretty much everybody that wanted to specialize eventually got what they wanted. Unless they were a terminal screw up (there are a few in every class) they were able to write their own ticket to some degree. I'd have to say that 50% of my class went straight, while another 30% pursued specialty after having been out of school for at least a year. Not every class is this loaded with specialty hopefuls, but I'd say that a large percentage of students from these schools look to specialize after graduation.
The truth of the matter is this...Every dental school that you go to is going to be competitive. Somewhere, somehow, there are always 'gunners' those that aim to be at the top of the class at all costs. And yes, specialty programs are pretty competitive and a solid class rank is vital to the success of gaining acceptance. So if a school has no grades, and no class rank, then aside from the letters of recommendation, personal statement, and CV, (all important, BTW) the end all be all of the application translates into the National Board Score part 1. You may think that this is unfair, but the truth of the matter is that few people slide by and get 'lucky' on the Board exams. There is so much accumulated knowledge that needs to be mastered in order to excel at this exam, that the ones that learned the material well during their first two years of D-school usually reflect this in their score. This is how residency directors standardize applications. Going to one of these schools (all of which have a stellar reputation with residency directors) is going to prepare you well for the board exam. Don't believe me? Just look at which schools have the highest averages on the part 1 national baords. They are usually the schools that I mentioned earlier. And by removing the factor of class rank, you needn't worry as much about how everybody else is doing. Just work hard and learn what you are supposed to. Things usually fall into place.
But in order to avoid being misled, here are some things that you should be aware of. The students at these schools usually have the same things in mind - specialty. They are going to work their butts off and this will without a doubt cause people to inadvertantly stress each other out and push each other to their limits. If you can see it for what it is worth, there is good and bad in this. You also don't HAVE to go to the mentioned schools to specialize. But once you enter the world of competition for class rank, all hell can break loose. You will usually end up killing yourself for that coveted top 10% and the truth of the matter is that if your board scores are somehow not up to snuff, your application will be substantially weakened anyhows. But if you go to a P/F school, only your board scores will cripple your application (or help for the matter). Are you starting to get the picture?
So to clarify things, there are a number of reasons that schools like UConn, Columbia, Harvard, and UCLA always place so many people into specialty programs (and believe me, they do). The specialty program directors give a lot of respect to those schools because they have produced many well prepared students in the past. And with the P/F system, every hard working dental student gets a shot at doing what they want. One last thing...Don't waltz into these schools thinking it's going to be a cakewalk...It is HARD work ANYWHERE you choose to go. If you slack off and cruise, it will show in your letters, board scores, and your reputation.
I can't tell anyone where to go to school, but if you have options, think about all the pros and cons, and figure out what you want to get out of dental school. If you are certain that you want to specialize (and to be honest, I can't see many people being certain of what they truly want without any practical experience) it might be a good investment to choose a P/F school. If you are able to be at the top of your class, then you'll probably be able to specialize regardless. But if you aren't the competitive type, think about a P/F program. It's not absolutely necessary, but trust me, it doesn't hurt. If you really feel stuck on a decision, feel free to ask. I'm not an expert, but having been through it, I think I have a pretty good idea of how the system really works.