Banner towing is almost all single engine fixed gear day VFR. If you are looking for an airline job this is not the kind of flight time that makes much difference.
If you are an MEI, and have a fair number of multi students, you night want to stay where you are. If most of your students are VFR, and you live in the North where flight schools come close to shutting down in the winter, and you are single, banner towing might be fun for the winter. Use the time to network to get a turbine co-pilot job.
Joe