If it's not strictly pass/fail like Harvard, UCSF, or UConn, you as might as well have grades than go to pseudo-pass/fail Columbia and UCLA with H/P/F. H/P/F may take off a little pressure as opposed to letter-grading but not nearly as much as strictly P/F does. The reason why letter-grading is more stressful is because you can be a single percentage away from getting an A and end up with a B. With H/P/F, the same situation can occur where you can be a single percentage point away from getting honors. Essentially, they're almost the same thing. The average exam score from Penn is an 85 (from word-of-mouth). At least at Penn, you get only ~1 exam (never more than 2) per week so each week you can dedicate to studying for only one exam. Big stress reduction in comparison to studying for 4 exams all in the same week. Instead of getting stabbed with 4 exams every so often you'll experience a dull but constant pain at Penn (~1/week).
If you're trying to decide between Columbia and Penn, Penn is more well-rounded (balanced with clinical and didactic) and Columbia focuses appreciably more on didactics with their medical school curriculum. If you were interested in OMFS, you should probably go to Columbia. Penn has everything a dental school could offer plus more. Penn ranks only the top ten. Everyone else is in eleventh place.
Both schools have a consistent record of around 30% of their students attending postgraduate specialty residencies. On paper, Columbia's top 1/3 tier as a whole would be considered as the equivalent to the top ten students at another school. At Penn, around twenty other students who were not top ten still matriculated to postgraduate specialty residencies.