When it comes to the '50s and '60s films, I find it hard to rate one over the other. For me, Godzilla, Battle in Outer Space, Atragon, Rodan, Monster Zero, War of the Gargantuas and many others are right up there with Forbidden Planet, The Day the Earth Stood Still, War of the Worlds, Them!, Creature from the Black Lagoon and the like. Both Japanese and American movies had this great sense of wonder to 'em back then.
In those days, the moon could have some lost civilisation hidden below its' surface, Mars was full of monsters, giant planet-killing space dragons roamed through the cosmic ether, highly-advanced beings held dominance over the Earth long before humans did, atomic radiation could create new life as well as destroy it and the rest of the universe was filled with unknown wonders and terrors. It certainly made for a lot of cool movies and shows to watch, that's fer sure.
As far as current stuff goes, I've paid very little attention to the Japanese side - save for various tokusatsu shows, Ultraman and so on. (not to mention bucketloads of anime

) And as for American shows, I enjoy the Stargates, Galacticas and the like, I'm not as crazy about 'em as the older stuff.
IMO the most enjoyable example of modern sci-fi on tv in recent years is Doctor Who, but that's British so it doesn't apply here.
