I would make two reservations.

One through hotels.com and a flexible AAA booking through hilton.com
Use reservation monitoring sites to see if your direct booking drops in price before you arrive and if it falls below an amount you're happy with you can rebook and cancel the hotels.com reservation.

Hotel pricing is anything but static and prices can change on an hourly basis at some properties. You'd be a sucker to lock in a rate now (especially if the res is months out) given how many tactical and regional promotions are around currently (eg: Hilton hotels in Thailand are up to 50% off AP right now).

However if you couldn't lock in a low, flexible AAA rate now I'd probably go with hotels.com purely for the extra benefits they offer since you have no hilton status (which would change your approach yet again).