Top Tier catchers in this free agent class
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Without question, the best catcher on the free agent market right now is Mitch Garver. A key cog in the Rangers' offense in 2023 that took them all the way to the World Series title, Garver slashed .270/.370/.500 with 19 homers in 87 games of work. In terms of offensively-inclined catchers, it is hard to get much better than that. One point in his favor is that Texas decided not to give Garver a qualifying offer, although he probably would have immediately signed it if they did.
There are some downsides with Garver, however. He isn't a particularly good defensive catcher which is exactly why he has been a back-up for the last several seasons despite his upside at the plate. His framing isn't particularly bad or anything, but he also isn't going to win any awards for his ability to steal strikes, either. There are also some platoon concerns as tough righties can give him some trouble. The ideal situation for him would be as a backup catcher who also sees significant time at DH.
Given that Garver is expected to get a two year deal in the neighborhood of $12-14 million this offseason, it would represent a significant investment on the Astros' part. Signing him shouldn't be considered likely as Yordan Alvarez is going to get as many plate appearances at DH as is humanly possible and Garver doesn't seem to have the defensive acumen to mentor Diaz. However, if Houston thinks having a guy like him spell Yordan from time to time would help keep Alvarez fresh in addition to backing Diaz up, it isn't completely impossible that the Astros could kick the tires here.