A straight up length of lead piping or a ball hammer would probably be better than a crowbar, because of the sticking issue.
The problem with baseball bats is not so much the weight, but rather that it simply doesn't concentrate the force of the blow in a small enough area. Basic physics people. The smaller the area force is applied to, the greater the force. Blows with baseball bats, if they do break the skull, are probably going to cause hairline fractures, but injuries that might knock a human unconscious, or cause them to die from cerebral haemorraghing aren't going to do shit to a zombie. It's very doubtful that a zombie CAN haemorraghe. No, you need to shatter their skull like a fucking soft boiled egg, and preferably slosh around a liberal quantity of brains to boot.