If you look at the best as the one that cost the most and will handle the most pellets at once then this is the best of the very best. Starting at $1600.00 and going to near $3000.00 depending on model. It will handle 4 (four) Pyrodex pellets.
In the hands of a capable marksman, the BP Xpress has fired 5 shot groups of one half inch at 100 yards and 3.75" at 500 yards.
http://www.ultimatefirearms.com/modelsprices.htm
Al