The few times that I have picked up cars late at night - the selection is pretty minimal. I saw a bunch of buick lacrosse and impala's etc.
I was going after an all wheel drive SUV and managed to get my hands on a trail blazer. I think the selection totally depends on what night you going to be there. I think thursday night is bad because a lot of rentals get returned and are not ready yet and similarly sunday night also.
Hope that helps.