... The reason I raise it is that they are not all born equal.
Others have already addressed the importance of aperture.
The quality of the figure of the mirror is obviously very, very important
as well ...
... But what I wanted to raise was the mounts themselves. Now and
then I've had to transport various new commercial mounts back
to the office to evaluate them as part of what we do.
I have to admit that I've even seen some 12" scope designs that
have been so bulky and awkward to transport in a car compared
to some other scopes with much larger apertures that looking
back in the rear view mirror I've asked myself, "what were the designers
thinking"
Related to this, another point I wanted to raise is the "feel" of the motion
of the scope as you slew it or nudge it or even re-focus it.
Those premium Dobs don't look the way they do just to look good.
The centre of gravity, the moments of inertia, the matching of the
amount of stiction and friction in their bearings have been calculated
and purposely engineered. It makes them feel smooth when you nudge
them.
This may seem a minor point but when you are looking at some faint
object at the limits of what you can discern, the last thing you want is
for the scope to hesitate when you nudge it, or overshoot the target
or have some undampened oscillation that you have to wait for to stop
before you start looking again. You are not seeing just with your eye,
but with your brain.
Until you experience it for the first time, it is hard to explain. But most
experience it for the first time when they are given the opportunity to
use someone else's premium Dob typically at a club new moon weekend
or at a star party ...
You even overhear it in the dark when someone might say whilst at the
eyepiece of someone else's scope, "God, I love this focuser".