Banner towing is aeronautical experience. It's neither good nor bad. Nobody is going to fault your hours towing banners. It's not a stellar background that leaps out, but it you're after flying quite a bit, that's what banner towers do; drone around the sky slowly, a lot.
I towed banners, like many others here. I started and ran a banner company. I can compare having done that to having done a lot of other kinds of flying, too. It is what it is. The panacea for springboarding to the airlines? No. It's a good seasonal job, and for someone who lacks the experience to do other jobs, it's not a bad option.
The oft-heard lament that "I don't want to instruct" is a cop-out, and attempts to compare banner towing to instructing or place one preferentially over the other are ridiculous. Each job you do will have merits, advantages, and disadvantages. I'd much rather have an applicant with a broad background from which he or she has learned to fly, than a one trick pony.