My Mk3 green stripe combo came loaded with an EV Force 12 speaker, not sure if original to the amp, but I kept it for about a minute. After trying a bunch of speakers I had around I quickly settled for a Celestion V30, which to my ears complements the amp perfectly and actually makes the small cab sound big and not boxy at all.
I used my SOB head with a 2x12 loaded with late ‘70s Celestion G12-80’s for a while, beautiful cleans, crisp and deep, but a bit strident and too edgy with gain. Much better with a pair of V30’s as well.
Greenbacks sound great with the 2 amps, in 4x12 and 4x12 cabs, but are a bit soft, especially with cleans.
I use those amps “on the edge”clean, with pedals for various levels of gain, so I do not use the channel switching on the Mk3 at all, although the rhythm and lead channels sounds great as well, it’s not my cup of tea.
What speakers do you guys use with your Marks?