Cons: I was overcharged and didn't realize it at the time. I reserved the car through CarRentals.com at a rate of $37/day. The salesman at the counter told me I could upgrade for $12/day and I agreed. I was charged $30/day more -- $67. When I turned in the car, they said they would email a receipt to me because their computers were down. I never received the receipt by email but my credit card was charged for the higher $67/day rate. I felt like the salesman was trying to upsell me. I will probably not use Avis again.
Pros: The rental car center at DFW is a somewhat longer than expected bus ride from your terminal, but busses seem to run on a regular basis. Once at the center, preferred customers are identified on a giant board with the space number marked and you just proceed to your car. Once you check out at the exit, you are on your way. Returns are just as easy, return to the center, get your receipt, and head toward the bus to your terminal.