Yeah, I think the fleets are similar. But sometimes the details and customer service can make a difference.
For our trip (tomorrow!), it came down between
Budget and Dollar and I had reservations with both. As I started to have some specific questions and issues I wanted answered, I found the Dollar website very lacking. Also, Budget doesn't charge for a second driver, if its a spouse (and often the spouse doesn't even have to sign the form or give their license #). Dollar does charge a fee for adding a spouse as a second driver (and requires they be present - although maybe in practice they don't push this). Then, I read here that Dollar, in particular, can make a hard sell for purchasing the additional insurance (and may ask for proof of insurance).
I actually called both companies at the locations we planned to pick up the car (hotels, not airports) with some specific questions, and Budget was great (but the Dollar lady was friendly too). I'm usually not picky about renting a car, but we have some special issues this trip. Budget assured me all our needs would be met and I've used them a lot in the past, so I felt very confident with them (and not as much with Dollar).
Alamo is generally my second favorite choice for car rental.
With this code I was able to get a good rate on Budget too: bcd x474200