Get letters from people who know you well and can write great letters. A great letter from an internist that knows you well is better than a form letter from a ortho chairman.
Also, letters from well know people, especially if they are personable, are the best letters. At many of my interviews, people just thumbed through the letters looking at who they were from, because that was the first and last time they ever looked at them.
I sent 2 ortho (1 well known, 1 nobody knew), but the letter from the guy nobody knew was the letter that everyone commented on, ir was so good. The remaining letter I sent was from a FP who knew me very well.
Good luck with the process!