For undergrad I think it depends on the class and what kind of study person you are. I find that I tend to learn a bit more and a bit better in smaller classes because the teacher has the time to field our questions better in class, my classmates pull together more to work through things, and our exams are usually not multiple choice. However, that does mean that I have to work a bit harder on the smaller classes than the large classes. If you just want to coast through and get the straight A's large classes may be the way to go as you are more likely to have multiple choice tests (although that varies depending on the school - most of my 150 people classes still have non-multiple choice tests, but my 200+ class did have MC tests and none of my less than 50 people classes have had MC tests).
But the quality of your overall education really is just what you put into the class. You get as much out of a class as you put into it. It's just sometimes a bit easier to access profs and other classmates in smaller classes because you get more "friendly" with everyone than in a large class.
