I can tell you that Howard Hanna has a large portion of the market share in the Doylestown and surrounding area meaning that many buyers and sellers entrust Howard Hanna to help them buy or sell. I currently have listings in Doylestown myself. You can find more information out at http://www.AmandaOndrey.com
As far as detailed information, any real estate broker/manager and/or the MLS should be able to provide that to you.
When you say 'top' agents, what exactly do you mean? Highest volume selling, buying, or both? Also, over what period of time? I would try a Google search to start, after that perhaps locate and contact the local MLS and see if they will provide you the information.