The version that get's current instance is part way to being the better version because it would be easier to use dependency injection & hence make it easier to unit test incase the logger writes to the db or sends email or otherwise interacts with some large external component that has behavior unrelated to the code under test.
On the other hand, if the goal is to encourage logging on your team, then logging with minimal set up is the better option, but config will be config file driven & you'd need a separate config file for tests vs production.
Also, in real life organizations, you can't always expect the operations people to be web config (or in this case Ent Lib config) super ninjas and sometimes you need to provide UI that turns on logging and turns off logging or otherwise changes the behavior (like sending errors to a different mailing list/list of users) and that will require dynamic config. I've worked in organizations when changing logging behavior via UI was just an ordinary transaction but changing so much as a character of the web.config took a frickin act of god and the change control board.