@CactuarJoe Invasion of the Star creatures was easily the worst.
I think my favorite watch (not favorite movie mind you) was Frankenstein vs. the Space Monster. Everyone involved in that one knew just what the movie was and still worked to make it as fun as they could. Dr. Nadir and the Princess were goddam ICONS. It was endlessly fun to riff on.
Devil Girl from Mars is up there too, only it's got some real dull stretches. All the great memes with Nyah are the kind of thing that makes #monsterdon so amazing.
My favorite movie was probably Forbidden Planet. It's just flat out one of my favorites in general.