If I’m not mistaken … doesn’t Dobsonian refer to the mount and Newtonian to the optical system?
I agree as to the mirror size: get the largest you can afford. It’s light-gathering ability you’re interested in, not magnification.
For a reflector, Newtonian is the simplest and most affordable optical system.
I have a fondness for equatorial/horseshoe mounts, but they’re best confined to permanent observatories. Dobsonian mounts are much easier to drag in and out of the garage.
What I don’t like about Dobsonians is not being able to use setting circles to find deep-sky objects. But, hey, life is full of trade-offs.
I really want a good scope with a tubular frame. We had one at my college’s observatory, and it was great!