Dempsey was for sure.
Wieters had a 1 really good year, but several others decent years behind the plate, that I would grade above a C, but thats just me.
I think Caleb was above average and ranks out a B most of the time, that nasty injury hurt and set him back some.
I think if you look at the stats, which IMO doesn't do the catcher enough justice:
Buster for SF has been pretty solid, his whole career.
Actually gets ranked #13 in the top 100 Catcher's list. Which is graded combined offensive and defense.
http://baseballegg.com/how-we-ranked-baseballs-greatest-players/baseballs-greatest-catchers-of-all-time/