J.T. Realmuto is the best catcher in baseball for the typical reasons. He can hit better than most backstops, with the eighth-highest OPS (.785) of 55 catchers since 2000 who logged 2,500 plate appearances. He can field better than most backstops, with the highest FanGraphs Defense metric among 34 catchers with 1,000 innings logged over the past three years.
And in terms of baser unning, there is perhaps no one better in the modern history of the game. Since 1950, 374 catchers qualify for playing time on FanGraphs statistical rankings for their "Base Running" metric, which is an "all encompassing base running statistic that turns stolen bases, caught stealings, and other base running plays (taking extra bases, being thrown out on the bases, etc) into runs above and below average." Guess who's No. 1, without a particularly close runner-up?
It's Realmuto, whose score of 18.4 is much higher than second-place Eli Marre