Speaking as a current 4her, the best SHOWMANSHIP breed in my opinion would be D'uccles. In my experience:
*They have been very tame and being a bantam, they are easy to control in the ring.
*For showmanship they give you the advantage of "extra" parts- feathered feet, vulture hocks, beards, muffs, AND a single comb that makes it easy to identify its parts.
*They are easy to find and only come in 7 varieties (easier to remember than OEGBs who have 28!)
Of course, go with what you know, I personally know Amerucanas best so I am in the ring with my black hen 98% of the time.
As for SHOWING, I find its a matter of what you can get your hands on. Good advice to go around and looking at local poultry clubs. I would also recommend Poultry Show Central to get in contact with some breeders and/or find some shows where you can get birds from (my current project birds are from a show I recently attended). If you have a certain breed you for sure know you want, look to see if their respective "clubs" have a breeder directory online.