Appreciably better experiences at one or another? I've had more mixed experiences with Budget but I"ve rented more from them and, except in one case, the worst experiences were at franchises vs. airport locations Used Enterprise just a couple of times (in part because they discourage one-way rentals with higher rates), but I do remember a USAA rep once telling me that Enterprise was good on resolution of any disputes regarding damages. I recall using Alamo just once, in Sacramento, and the experience was just fine (got a Dodge Charter as a full-size car), though I've read some negative reviews of the company. Renting either in Charlotte or Greenville, Budget is the only one that would charge more for an additional driver even if it was my spouse (the rep at CLT said the charge was $13.99 a day with a max per rental of $99, though the Web site says the max charge is $65).
For picking up at CLT and returning it to CLT, prices at all three are about the same, whether I use a Costco or AARP discount code (Avis and Hertz would cost appreciably more). If we picked up at CLT and returned to GSP, Budget would be cheapest (in fact, the only one that wouldn't charge more for that one-way rental).