For what it's worth (which is very little, I know), my favorite box art is for this boxing of the Heller F6F Hellcat.
I had a friend years ago who was an exceptional aviation artist. Sadly he lost his life before he would see professional success, but he told me about his approach to choosing a vantage point from which to draw aircraft. His intent was to capture an aircraft's character, which was the angle or attribute that makes a particular aircraft distinctive, different from all the others. You can imagine any number of examples. If you were to draw or paint an F-8 Crusader you'd probably want to show its unique wing. The F-16 looks its best when all buttoned up and sleek. The B-2 Spirit is all about its being nothing but wing. You get the idea.
It's with that mindset that I've enjoyed box art over the years, and that's why Heller's F6F has always remained at the front of my mind. It shows the Hellcat at its best angle. You can see its chunky fuselage, the sight gull wing design. The plane is weathered, has character. The pilot is even looking at you.
The F6F isn't anywhere near the top of my list of favorite airplanes, but I love this box art. What's your favorite?