version looks nice... If you are targeting Perl 5.9 or greater. 5.8 is still very common in the wild, which may be a reason many module authors avoid it. (It's why I do.) Of course, you can list version as a dependency, but that adds another step to the install and complicates things for the user.
I personally use the numeric X.YYZZ format, meaning version X.YY.ZZ, as the most compatible format at the moment. (And I let ModuleMaker set it up in a BEGIN block, as that's easy.)
Really, it comes down to: Pick whatever you feel comfortable with that doesn't cause problems for your users. v-strings cause problems. version is a minor annoyance for anything earlier than 5.9. Numeric seems to cause me the least amount of headaches, but that's me.