I'm assuming you are talking about college recommendations for medical school, right?

If so, then you obviously want to do well in the class, and it's obviously good if you know the teacher as well. I'm trying to remember who I had do my letters - I think I had my advisor in my major, one of the professors I did research with, and then one teacher from a small non-science class where I felt I did well, and I felt the teacher knew me. Obviously, in all 3 cases, the teachers knew me fairly well.

Letters are HUGE if the prof (or other recommendation writer) knows you well, and can give specific reasons that you are a swell applicant. However, even the most impressive recommendation source is of dubious worth if they don't have anything specific to say, other than "Jojo Bucklewhip earned an A-minus in my Chemistry class, and ranked 12th out of 575 students." I mean, hip-hip for you, Jojo, but who CARES?

My letters came from academic sources (my college chem professor and my grad school thesis advisor), military sources (my battalion surgeon and my leading petty officer), and other medical sources (docs with whom I had worked in a volunteer setting, etc.). This made for a nice patchwork of recommendations... but if any of these people hadn't known me very well, I would have dropped them from the list in an instant.

For profs, I would recommend doing well in the class, AND getting to know them! (Preferably WITHOUT being a total suck-up, because they can see that a mile away and tend to hate it... wouldn't you?). The best way I found to do that was to ask good questions, attend office hours once in a while, and generally get to know the prof a little bit.

I mean, profs ARE people, right? One of my physics professors was a marathon runner, and I was training for a marathon during that semester. We talked about training and running shoes, in addition to physics. At the end of the semester, the guy knew me. If he hadn't left for greener academic pastures elsewhere while I was deployed with the military, I am sure that he would have written a fine letter, because we got along, I did fine in his course, and he knew I wasn't just talking to him to get "the recommendation."

Finally, "other" recommendations from physicians or employers can also be effective in your application, if they make sense. Military leadership was key for my app, but not everybody has that. Whatever you have as a background, whatever cool stuff you have done, try to find someone who mentored you along the way, and see if they feel comfortable cutting you a letter.

Good luck!