PIMA for sure and not just for the museum, I saw 5 A-10's in formation that day, F-16's, Apache's and a EC-130H.
Udvar Hazy center because of the rare German WWII stuff. It's also nice to be able to look down from the walkway and see the topsides of some of the aircraft. Having never seen an F-14 fly, this view really gave me an appreciation of the shape and size of the beast.
I also recommend the outdoor museum at Palmdale, CA, because where else can you see an A-12 and a SR-71 side by side? There is also the worlds only B-52F on display. I was there on a Sunday and the guide who opened up the museum was super nice guy, we bonded over our experiences with hard drinking Australians (he served in Vietnam on the same base as Australian Canberra crews).