My favorites are the ones that I wanted for years, and then someone finally manufactured them. A few years back AMT did the YB-35 and the XB-70. It was a rush when the canopy masking came off and a real finished model was sitting on the bench!
Another favorite is this Aurora Lockheed XFV-1 . I bought a huge box of junk for $1.00 at a flea market. It included the XFV-1, some Convair airliners, an Aurora Blue Knight, etc. The XFV had no tail or propellers, and the canopy was painted over. I scratch built the tail, borrowed a prop from a Lindberg Pogo, polished the canopy, and had a rare bird in my collection.
Just Build a Model For The Fun of It!
Gerald