I was in your shoes last year and had the same questions. I eventually decided on ranking one prelim spot and ended up matching there. How beneficial was this? I don't know yet because I'm in the middle of the application process like you are. But here's why I did it: I didn't want to take the risk of ending up at a crappy prelim. Yes, they're easy to scramble into. But how easy is it to scramble into a good program? Not so easy. I felt that it would benefit me more to do a prelim year at a "big name" program, obviously, so it would be safer for me to rank.
But I also took into account that I was a less than stellar applicant and there was a good chance I wouldn't match into ortho. So I went with the safety valve and I'm glad I did. I don't know if it's better than a year of research or anything else, but at least I didn't end up wasting a year at some small program which wouldn't increase my chances of matching when I re-applied. I don't know how much truth there is to this, but that's what I feel.
