I have only been to Gatwick. Nice place. Smooth operation. Two nice ladies operating the room. Strict but not unpleasant at all. Excellent personnel restaurant and free wi-fi access everywhere.
The room was never full, so small chance of refused booking/move to second choice.
There are lots of cheap accommodations nearby with easy transfer to CAA. Free bus from the terminals.
Your choice should be the place that gives you as little travel as possible and good accommodation with internet access.