Each area is a bit different. Before "Katy stole the door", I had Sea Tow as well as BoatUS. Reason: their "home territories" were somewhat different, even though there was an about 50% overlap. In the overlap zone, it meant that if I had a problem on a busy day, I might not need to "wait my turn". The non-overlap zones were important, as those areas were the distant areas from my dock. A non-covered tow would have been pricey.
A moderate bit of research on the territories, and how they handle it might be valuable.
Note that "down heah", we have never had an overabundance of tow services. I suspect that in VA, you have adjoining franchises for each of the company providing a more consistent coverage of your area. Be sure to check out the degree of "farther out coverage" if you tend to take excursions out into the deep briny.