I cant speak of the 6" as i have never used one... I do however own the 8" and can sing its praise on high!
a more wonderful scope (for the price) you will not find.
8" under your dark skies gives you a galaxy hunter!
of course if a 12" you can afford then a 12" you should get if transportation is not a problem. aperture rules the day!
if you are considering astrophotographt in the near future then dont get a dob at all, as you will need an equatorially mounted telescope
hope i have helped. and welcome aboard.