if you do use screws make sure to get pan head as to not damage the sub. however, a more practical approach would be to get some hurricane nuts and bolt the sub that way. when using screws, if you continuously mount and unmount the subs you'll eventually strip it and the screws will become useless and you'll have to replace the baffle.
If you're going to use pan head screw, deep/coarse threads are the way to go...I'd just get some a little longer so that they'll go all the way through the baffle.