Which came first...

[Bry_Sinclair]

...the Nebula or the Galaxy?

Given the very similar spaceframe I'd suspect they were being developed at the same time, though I think the Nebula would be the first out of dry-dock so as to be a testbed for technologies used in the Galaxy.

 

[Timo]

The Nebulas have lower registries in evidence, and while it's arguable whether the registry for USS Galaxy really is solid canon, some Nebula ones do go below that.

However, I rather like to think that Nebula was the definitive product, and Galaxy was just an outgrowth, a luxury version built for special duties that didn't really call for all the bells and whistles but benefited from the ship tingling with those. That is, sometimes Starfleet would want to send a ship that was just plain awesome, and the Galaxy would be it.

But the Nebula would do the real work for ships in that size category, and would exist in a great number of variants, as seen - some with Galaxy-like components, some without. Although whether the bolting on of a Galaxy saucer with the impulse engines faired over was a functional choice, resulting from testing that advanced hardware on that other class, or an economic one, applying an available even if non-optimal design... Well, the engines were faired over on the likes of the Bonchune.

Timo Saloniemi

 

[Unicron]

It's possible they were developed simultaneously, once the technological advancements intended for both designs were considered viable and construction was ready. The Nebula is essentially an upgrade of the older Miranda series vessels.

 

[Dukhat]

I’ve always felt that the Galaxy class herself was the last type of ship designed for the ‘Galaxy family’ (i.e. the Galaxy, Nebula, Cheyenne, New Orleans, Challenger, Springfield, Olympic, and possibly Freedom classes, along with some of the conjectural classes that have similar registries but no design associated with them, such as the Andromeda, Chimera, Korolev, Rigel, Sequoia, and Zodiac classes), and that it was the largest. Then the next generation of ship classes started, such as the Sovereign, Intrepid, Prometheus, Nova and the conjectural Bradbury class.