I've stayed in the Holiday Inn Express Crawley a few years ago. It was OK, but a 10 minute walk to Three Bridges station and then one stop to Gatwick station.
I've stayed at the Holiday Inn Gatwick which is closer to the terminals, but still meant getting a bus. I don't like waiting for buses at the best of times, but I hate it at 5.30am.
When I'm travelling on my own, I prefer to use the Bloc hotel. You get a very small room - the bed takes up half the area of the bedroom. It has a nice double bed, a decent shower and really good towels, and its in the South terminal building which means its brilliant for an early start or late finish. Check in is quick, and there is nothing to do on checkout apart from dropping the key card in a box.
I also used the Yotel which is also in the South terminal, but it was showing its age. I had one night in the Hampton in the North terminal. It was OK, and a full size room, but I wouldn't pay more for than the Bloc. I recently had a night at the Premier Inn which is across the road from the North terminal. It was a reasonable price, the room was fine and the location is good. I really appreciated being able to walk there rather than relying a bus transfer.
For an airport hotel, I want something which is close to the terminal. I don't care about breakfast as I'd rather get it in the departure lounge, or station. I want fast check in, a quiet room with a bed and a shower.