There's a few with some tight continuity. As far as what Hulu has, here's what needs to be viewed in order:
The Heisei Series
These movies try to have strict continuity, despite how much they flub it up and don't use it. But for the sake of consistency it's best to watch them in order. It's important to note that the first two films made for this continuity are not on Hulu (The Return of Godzilla & Godzilla vs. Biollante). So you'll have to go in to it with the understanding that a new Godzilla has appeared twice since 1984--And before that only the events of the original 1954 film had taken place:
Godzilla vs. King Ghidorah
Godzilla vs. Mothra
Godzilla vs. MechaGodzilla II
Godzilla vs. SpaceGodzilla
Godzilla vs. Destoroyah
The Millennium Series
The Millennium movies are an anthology series with no continuity between them. With the exception of two films, the only connection they generally have is to the 1954 original. Any important information from the original film is usually recapped in some way. You can watch any of the following in any order you wish. But this is the order they were released:
Godzilla 2000
Godzilla vs. Megaguirus
Godzilla, Mothra, King Ghidorah: Giant Monsters All-Out Attack
Godzilla: Final Wars
The Kiryu Saga
The two Millennium movies I spoke of that were the exception are usually dubbed "The Kiryu Saga" or "Kiryu Duology" by fans. Like the other Millennium movies, they're sequels to the original Godzilla and some other Toho kaiju flicks. Again, pertinent information is recapped via flashbacks:
Godzilla against MechaGodzilla
Godzilla: Tokyo SOS
I generally consider Godzilla vs. SpaceGodzilla the worst of the entire series and Godzilla vs. Megaguirus and Godzilla Final Wars aren't too far behind. I know many who would disagree, but I come at the series from a very different perspective than most. The 1998 movie is a borderline taboo subject among the fandom, so we usually just ignore it.
But, as with anything, try them all out. Tastes vary and I have no idea what you might be looking for in these flicks.
"'Nostalgic' does not equal 'good,' and 'standards' does not equal 'elitism.'" "Being offended is inevitable. Living offended is your choice."