I have Budget Fastbreak, and I am also an Alamo Insider. These programs will save you a ton of time, whichever way you go.
I disagree about not being able to use the kiosks with a Costco reservation. I've done it lots of times. The trick is to log into your Alamo Insider account before you arrive, and try to prepay things. Print your confirmation code and documents, and when you get to the kiosk, scan that code, and you're off and running in a minute or two. It's not difficult.
With Budget Fastbreak, as long as your Fastbreak number is included on your reservation, they'll have your paperwork waiting for you. They have a separate line for Budget Fastbreak customers, so the most you'll wait is behind any other Fastbreak customers who happen to be in front of you. Since the credit card and such is already registered, you'll have your paperwork in seconds. I once passed by 34 people (I counted) waiting in the regular line for their car, as I went to the counter with no Fastbreak line at all. As we drove off the lot, I glanced over, and the same person was still waiting at the front of the line that had been there when we walked up. It is a HUGE timesaver.
Dave