租車請教--8月初去黃石公園一帶。需在Jackson Hole 租車。請問：

1）Which method do you recommend? go thru Priceline, Expedia or directly call the car rental Co (Alamo, Avis, etc) @Jackson Hole, Wy? Any price difference?
2) Do I need to rent the car right now, or I wait a little? Does time make a difference on rental price?
3) Is a full size car good enough to go to Yellowstone and Mt. Rushmore for a family of 4?

Many thanks in advance for your time and your help