When he was at his best, George Gibson was the best. From 1908-1912, Moon was among the premier catchers of the league -- a who's who of National League catchers with the likes of Kling, Meyers and Bresnahan.
Of the four men, Gibson yields the lowest career batting average and RBI total; anecdotally, it is said that Gibson could be counted on for hits when they counted, however. It was, of course, Gibson's defense and ability to handle pitchers that kept him in the conversation. From 1907-10, Gibson led the NL in games played by catcher. In 1909, 1910 and 1912 he was tops in the NL in fielding percentage. In 1909 and 1910 he caught the most base stealers in the NL (while also allowing the most base stealers in 1910). For his career, he's 10th for base stealers caught and 33rd among catchers in double plays turned.
Interestingly, from 1905-1913, one of these four men backstopped the National League representative in the World Series.
Of the four, only Roger Bresnahan has been elected to the Baseball Hall of Fame in Cooperstown (a quick read on Wikipedia has a quote from Bill James suggesting that his election was a mistake).
But the Canadian Baseball Hall of Fame wasn't about to forget about George Gibson. He was inducted post-humously, in 1987, along with Fergie Jenkins, Rockey Nelson and Russ Ford. The image included in this post is the cover of the program from Gibson's induction. I picked it up recently and it's in very good condition. I was hesitant to scan any of this inside because I didn't want to crack the spine -- the contents are mostly ads, with a one-page bio of each player. Gibson's page contains the same information that is on his plaque at the hall...which you can see if you're ever in St. Mary's. Seriously, it's not a huge museum, but if you're ever in the area it's worth the visit. If you have some time right now, actually, it's worth visiting their site to check out what they've got going on, including their plans for a new, bigger, museum.