Hi, I have a Dr.Z Carmen Ghia head (18watt el84), I use as a almost clean platform for my OD pedals with a mojotone 1x12 (20" x 26" x 10-3/4" ) with three pieces convertible back. Now i have a G12H30 in my cab and sometimes it gets boomy and hollow at higher gain especially in small spaces.
I play from blues to hard rock and I want to get a very classic/standard british tone with tight bass when I go higher gain, but good complexity when i go for Hendrix Axis-type tones.
Which speaker should I choose? Should I keep the back of the cab closed?
Sounds like either the full-on classic Green Beret ... or, if you want a little more headroom and solid bottom, an Invader. Either choice will achieve your stated Objective of:
"I want to get a very classic/standard British tone with tight bass when I go higher gain, but good complexity when i go for Hendrix Axis-type tones."