Interesting, Jackal -- I can tell you do have an exhaustive knowledge of Dollar/Thrifty.
A corporate/franchise city-by-city chart would be marginally useful, I guess. Maybe I'm wrong, but I would book with the corporate side if everything else was equal (which it usually is!).
Right now, the only reason I prefer one to the other is that I try to remember to book with a cashback site and when I pull up the data from a site like evreward.com, the payouts can be different. BTW, I'm not even sure I get the cashback, because it's usually so little money (less than a dollar a day) that I don't bother to to check or follow-up.