Invasion of the Astro-Monster/Godzilla X Monster Zero ended up being a real treat for me because I didn't ever see the movie until after I saw episodes of The Rebel on television. Nick Adams is the actor that plays the American in the movie and in The Rebel he's a man named Johnny Yuma roaming the country side with a sawed off shotgun doing cowboy shit. The entire time I watched Monster Zero, I couldn't help but imagine Nick Adams character was an astronaut Johnny Yuma.
You're starting to get to the point where the Showa era starts to let loose a bit more and have more fun. It's honestly been so long since I've seen either Godzilla X Ebirah or Son of Godzilla that I don't remember much of either. They're all fun in their own way though. Lots of people really enjoy Godzilla's Revenge and Godzilla X Hedorah just because they're pretty wild departures from your regular films.
So, out of curiosity, do you have a favorite monster yet?