right now via Costco site is about $50 cheaper all in vs the others.

As you know if you did this in the past car rental prices change daily if not a couple times a day. I haven't rented with Avis for a long time. I do know Dollar and Alamo and I do know one day I will check and get a fantastic rate, but that might last 4 hours. So no matter who you go with be prepared to book right away. You can always cancel and book over when and if the price drops again.