Without really defining "best hitter" I would say Joe Maurer, Brian McCann and Buster Posey. I saw all 3 of them batting in the 3-4-5 spots in the playoffs. The next question is, can you name 3 OTHER catchers who are the best hitters on their team. I can't. Historically many catchers hit like crap and batted 8th or 9th depending on whether they were in the NL or AL, but lately some of them are hitting. I heard an old timer on an old timey retrospective show complaining that Johnny Bench ruined it for catchers because he could hit. Before that catchers didn't need to hit. Then Piazza broke a lot of Bench's offensive stats for catchers, and people started to complain about his defense, instead of acknowledging him as the best hitting catcher of all time.
If baseball is really the sum of a whole bunch of little things that make little differences, maybe the good hitting catcher is undervalued. When I searched at MLB.com "OPS for catchers", another playoff catcher came up near the top, Carlos Ruiz. Now I wouldn't say he is the best hitter on his team, but he is a good hitter. Last year a case could be made that Suzuki was the A's best hitter. Maybe next year he turns it around a little, and that boost plus a couple of outfielders gets the A's into the playoffs.