If you are a recent college grad, I think it is okay to use a direct supervisor and an old college professor.
I am 23 and my 3 recs are:
1) direct supervisor at work
2) professor from school
3) peer at my startup
If your professors worked with you on a variety of projects or knows you very well then I think his or her rec would suit you better than a rec from a supervisor during a two month internship. At the end of the day, the person who will put in the most time/thought into your rec should be your best bet.
Agreed. From my conversation with adCom's and alums, I heard over and over how too many people just try to name-drop for this (especially with random alumni that got their masters from the university in something besides an MBA) and don't use people that are actually familiar with their background and can speak to it. The recommendation forms don't in any way ask your recommender what their experience is or where they went to school, just their relationship to you, the applicant.
The 'direct supervisor' rec will take care of all the basics (are you responsible, are you considerate etc etc). Use the 2nd one for someone who knows 'your story' and can give the committee an idea of who you are as a person.