Towing banners is a lot of fun, some will tell you its a bad way to build time since its all VFR day but I could care less what they say. I'm not trying to make myself look good on paper for the regionals or whatever, just trying to have a good time.
I will say that if you have no experience towing banners but at least have your TW endorsement, there are still some companies that will hire you. Only problem is the pay is likely to be $12/hr or less, crappy planes/mx, etc. I worked at a company like this and while it was fun it was pretty scary sometimes. Not sure I would recommend this route for everyone. Knowing what I do now I'd saw try for van wagner and if you dont get it maybe keep instructing or something else. Not many companies are this professional. We even get paid when a flight gets cancelled for weather or MX!