So, 3 years after graduating and several years in the "real world," I've decided to finally apply to grad schools. I know it's early in the process to be thinking about this, but I'm trying to figure out who to ask for rec letters. My first two are easy--the first is my main research adviser, who I worked with for two years and did my senior thesis with; the other is my REU adviser, with whom I have a 2nd-author publication in a respected journal. I've let both know I'll be submitting applications in the fall and both say they'll be "very happy" to write "strong" recs for me.
My problem is with my third rec letter. I have a couple not-so-great possibilities, and this is complicated by the fact that I haven't kept in touch with these more tangential profs. The first option is a professor I took a class with, in which I did very well, but otherwise haven't had much contact with (even when I was in school). He wrote some rec letters when I was applying to REUs, but I feel like his contribution doesn't make as much sense this long after graduation.
My other option is my major academic adviser--I never took any classes with him, but he was in the same research group I was a part of, and I feel that he could give a "big picture" take on me, especially if I provide some supporting documentation. He's also got a slightly bigger name in the field.
Does anyone else have any experience with this situation? Any ideas? I've read through most of the threads in this sub-forum and this doesn't seem to have been discussed before.