Well, basically it is a matter of preference, but I prefer the version with the v, as Semver does it that way and I try to follow that specification as close as possible to get a sane versioning.
It also makes filtering for those Tags easier, as you can press v and then the TAB-key for autocompletion: This will list all the tags (and maybe a few branches), whereas there are several digits a tag could start with.
Edit: In 2019, Semver added a section to their FAQ, clarifying that the “v” prefix is “a common way to indicate a version number” (see “Is “v1.2.3” a semantic version?”).
See also: Is there a standard naming convention for git tags?