Aaron
4 x 4 minimum I would say.
look at the web site Mark has put; this one is the best and helpful.

You need to balance the need for luggage to & from the airport with a car suitable for the rest of your holiday. No point having a massive car for luggage trip for 2 days. But that may mean having dome smaller cases inside.
A premium 4 door like a Pacifica would be ideal, subject to the luggage point.

Bear in mind that US saloons do have a very narrow lid to their boot/trunk, although deep. That's why I suggest making a point of a pacifica type although its in a saloon section, as its a 4x4. To ensure a 4x4 you may need to specify mid size SUV.
Also depends what car hire you book with as not many allow you to actually specify the actual car; Alamo let you pick from a line, Dollar specify the car only when you arrive, although you can change it when you see what you have been allotted. Other firms I have no knowledge of.

(or you could get a HUMMER!