On my EM rotations, I gave my SLORs to both EM faculty (student rotation directors and other EM faculty) and a program director. The CORD website (
http://www.cordem.org/slor.htm) has the SLOR for you in Word (good for having on disk or attached to an email since they can fill it out on their computer), PDF (prints out nicely if they want to fill it out with pen or typewriter), and Internet Explorer (also good for filling out on the computer) format. Most faculty familiar with the SLOR will know what to do and have their own preferences, but I went ahead and supplied them with a copy of it to make it easier for them.
They state on that CORD website, "ONLY Emergency Medicine Faculty are to complete the SLOR. Most programs with student clerkships are encouraged to have the Student Clerkship Director and/or the Program Director do a SLOR." Many of the clerkship/rotation directors will do a composite of what the various attendings you worked with said on your evals. I usually asked faculty with whom I worked with 2 or more shifts (including those that I felt I got along with and those that seemed like nice people who wouldn't do anything to hurt your chances) if they "felt they knew me well enough to write me a strong letter." I didn't want to get a subpar letter (and that would be a waste of their time) so I was giving them an out so that they could say "I guess I didn't work with you enough" if they couldn't say good things on the SLOR. I got more than the required 3 or 4 letters so that I could rotate which letters I sent to the different programs I applied to (an idea I got from studentdoctor.net). I don't know if it mattered, but I guess it couldn't hurt if you have that choice.
Also, you can try to schedule or switch shifts so that you work enough shifts with the PD, chair (if they are in the ED much), or a certain faculty member (I asked residents who would be a good person to get a SLOR from). I usually requested an appointment outside of shifts to meet and discuss getting a letter so that I could chat and provide my CV, PS, and other info. When I asked one person who I had 2 shifts with for a SLOR, he said he would be happy to and wanted to know if I would be working with him any more. I did have another shift so he wanted to wait until afterwards. During that last shift, he seemed to ask more questions and pay more attention. I got some questions right and some wrong, but I don't think that hurt me any. I assume he just wanted to see how I was thinking through those topics and it gave him something to write about (hopefully mainly good stuff!). The point is that if you let people know early that you are interested in EM and would like a SLOR (which everyone understands; it's part of being in academics for them and part of the applications process we have to go through), then that helps to get them to pay more attention to you.
Good luck! There's a lot of stuff to do up until match day, but it's all worth it.
-ak