<p>I am applying for Computer Science PhD for Fall 2007.</p>
<p>I already have 2 prof that I worked with willing to write recommendation letters for me.</p>
<p>For the third one, is it better to ask a prof, whom I only have contact from a class that I got an A or from a post-doc that I worked with?</p>
<p>It's generally better to get letters from people who know you well rather than from people who know you only superficially.</p>
<p>I had a letter from a postdoc, and I got into my top-choice school. :) If you are still concerned, perhaps you could go speak to one of the professors who's already writing you a letter and ask his/her opinion on the matter.</p>