You tell me: Small Group Instruction Led By A Teacher vs. Peer Group Learning?

Which method is better? Or, are both methods equally important?  If a child receives small group instruction from a teacher would they have a higher understanding of the math skills?  Would peer group learning be the best option to help students reach a higher understanding of math at a faster rate than small group instruction?

I have used both methods in my classroom.   I've noticed that they tend to be happier when learning from each other.  On the other hand, when I do small group instruction, I tend to hear lots of "Aha Moments"!  What are your thoughts about this subject?