Maybe at another time in aviation history, banner towing wasn't the best option out there. I admit, I wouldn't know. I'm fairly young and new to this. However, I'm intimately familiar with the hiring climate of today, and what the regional airlines are looking for in a pilot. If you have 1500 hours and can fog a mirror, you've got all the experience they're looking for. In this sense, whatever gets you to 1500 hours is the quickest is indeed the best solution, with seniority playing such a large factor in your quality of life at the airlines.
Now I will say, 121 flights are going to be IFR 100% of the time. Everyone knows this. Banner towing will get you absolutely zero instrument time (legal and logable instrument time, that is
). So you've gotta be instrument current and proficient. Can you fly banners for three months in the summer, keep instrument current and proficient in the winter while working on other ratings such as CFI, CFII, MEI and getting xc/night time(while also attending college possibly)? Absolutely. Will this give you a wider variety of experience than just instructing? For sure. You'll certainly be a far better stick than you were before you started. And you'll have a ton of fun doing it.
As the saying goes, there's more than one way to skin a cat. If you're young, have free summers, and are looking to fly your pants off to get to the regionals, it doesn't get too much better than draggin' rags. If instructing is more your thing, nothin wrong with that route mate. My qualm simply lies with guys who don't hold back on saying banner time is useless flight time. It just aint true.