Used Alamo in October, used online check-in and added the extra driver info at that time. Printed the paperwork before we left. Upon arrival, just went out to the garage, had a full size booked. Picked our vehicle (keys inside) and drove it to the exit, handed the attendant my paperwork, my CC and both our drivers licences. I don't even think he looked at the paperwork, just scanned our licences and verified my CC and we were on our way. Maybe 10 minutes from picking up our luggage to driving out of the parking garage.
Definitely recommend the online check-in, think you have to be an Insider member but thats free anyway.