I think on an artistic level the original is untouchable,simply a great piece of cinema with far more intelligence and depth than anyone ought to expect from a 'monster movie.It's really about the atomic bomb!!
Howvere despite this it isn't that entertaining,so I would go with somebody else on this thread and mention the semi-trilogy of G V M,GTTHM and MZ,made at the height of Toho's Golden Age.Good plots[often rehashed],a sense of humour without descending into complete campness,impressive effects,wonderful monster battles and great human characters well acted whom you'll happy to watch while you're waiting for the monsters.Toho had such a good stock company of actors then.I suppose G V M is the best all-round film for entertainment but seeing Godzilla,Rodan and Mothra team up against Ghidorah is my favourite climax to any G film,it's so rousing.
Also really like DAM ,KK V G[Japanese version]and TOM,hel,I like ,em all!!