There is no such thing, and it would not matter anyway. Here is why.
It is not so important whether you get a patent, but whether it would provide wide coverage/scope, to make it useful and profitable.   Many companies (particularly in Japan) "collect" very narrow patents, covering only the very specific narrow improvements.       
In addition, most patent applications are dropped because of cost; not because they are unpatentable.
Finally, I could tell you the most expensive patent attorneys, but does it mean they are the best?  Absolutely not.  The best patent attorney is the one that will take time to work with you to get the best results, within your budget.  
Hope this helps. 
 
-Daniel Basov
Solton Rosen & Balakhovsky LLP
110 Wall Street, 11th floor
New York, NY 10005
212-344-1744
www.srblaw.net