Potential Post-Doc supervisor visit: should I give a talk or just have a meeting?
Unless told you shouldn't, you should always opt to give a talk under such circumstances. It makes discussions with your potential future advisor and group members much more meaningful, because your interviewers now have a much better sense of what you do. 

Moreover, a solid presentation of technically sound research shows that you have achieved one of the most important skills needed for a researcher: the ability to effectively communicate your work! As a postdoc, your advisor is going to expect you to have most of the research skills needed to complete your work with minimal supervision. Giving a good presentation will clearly demonstrate most of your credentials in a way that a face-to-face talk will not.

Finally, giving a talk to a (mostly) friendly audience is always good practice for your future career. (People get better at giving presentations by giving presentations!)