What are considered the main universes of the DC Universe?

[Restingvoice]

New Earth also called EARTH-0 is the current main universe.
You'll find the list of all the Earths and domains of the gods in the map of current multiverse here
The current Multiverse is the evolution of previous Multiverse.
The first Multiverse had an infinite number of Earth.
That ended with Crisis of Infinite Earths where they made that there's only one Earth.
Then they brought the Multiverse concept back.

[Bored at 3:00AM]

The revisions to some of the longer lasting characters is part of what made this whole multiverse thing messy.

For instance, while the early Superman stories didn't explicitly rule out the idea of the character having had costumed adventures in his youth, the Superboy stories contradicted some things established in earlier stories. Among these were the look of Superman's original costume, his original power set, when he learned of his alien heritage, and when he first encountered both Lex Luthor, and Kryptonite.

Some of other characters who weren't cancelled between 1950-1956 had similar canonical issues. Batman's butler Alfred was introduced years after Batman's debut, but as time passed, Alfred morphed into being a Wayne family retainer whose service predated Batman's birth. Aquaman was originally mutated by his human father, but later was characterized as an exiled prince of Atlantis.

The thing you have to remember is that nobody was really keeping careful track of all this historical canon, or thinking out the implications of all this world building because they assumed they'd have 100% customer turnover every few years. In the minds of DC's editors and publishers, their customers were boys of about 5-12 years old, who would drop the product when they aged beyond that, and were being constantly replaced by a new batch of younger boys. It wasn't until the early 1980s that DC seemed to catch on to the idea that the median age of their readers was increasing.

What's more, this aging customer base remembered the past. Even those who hadn't been around for the originals were starting to hunt down and collect back issues. The fans, and perhaps especially, the fans that became comicbook creators themselves, began to try reconciling all of this disparate stuff into a coherent history. Roy Thomas was probably the most consistent writer pursuing that goal, although he was hardly alone.

Yeah, the very concept of a consistent continuity didn't seem to even occur to DC until the late 1950s...

[Aahz]

Some of other characters who weren't cancelled between 1950-1956 had similar canonical issues. Batman's butler Alfred was introduced years after Batman's debut, but as time passed, Alfred morphed into being a Wayne family retainer whose service predated Batman's birth.

That actally didn't happen untill COIE (and I tink even then he became the Butler after Bruce Birth).

But there have some other wired stories pre crisis, for example with Bruce and Clark meeting as teenagers (and in some of them his parents were iirc still alive) or Bruce being the first Robin.

[Denirac]

I still call New Earth the MAIN Universe because I dont really care for the Numbers