Hi picnic,
I have experimented with a number of speakers in and out of my LSS, as well as with my Blue Angel, and for now, I favor two (2) Celestion Golds in an external, closed back Zinky 2x12 cabinet.
My second choice for the LSS after the Golds, and after all my experimentation turned out to be the stock LSS Mesa Black Shadow, which surprised me. I take this result as a testament to the insight and expertise the Mesa folks have, and exercise in their speaker choices, speaker designs, and amplifier pairings. I think the Mesa folks are amazing, and appreciate their expertise.
I am playing Les Paul or Les Paul type guitars with Seymour Duncan or EMG humbuckers. I wired the tests so I could hear both speakers at once with one on my left and one on my right, and/or, so I could A/B back and forth between the speakers with only one speaker on at a time.
To date I have compared these 12 inch speakers:
Eminence Cannabis Rex
Eminence Legend 1258
Eminence Red White and Blue
Eminence The Wizard
Eminence Zinky 12” Custom Speakers
Fane AXA12
Fane 50 watt, no clear model markings, made in 1978
Celestion Vintage 30 in 2x12 closed back
Celestion Vintage 30 in 4x12 closed back
Celestion GM12 Greenback
Celestion G12-T75
Celestion Alnico Golds
Mesa Black Shadow (the stock LSS speaker)
From this experimentation I learned that each of these speakers can work with the LSS, and as different as some of these speakers sounded, I enjoyed the tone nuances that each provided. I really didn’t find any undesirable speakers or tones, just differences. I also learned that the tone controls on the LSS are extremely responsive and because of this, could mold the LSS sound to coerce pleasant tones and good response from each of these speakers.
So far, though, my favorite configuration for the Lone Star Special is a Zinky 2x12 cabinet with two (2) Celestion Alnico Golds. To my ear, the Golds in the closed back Zinky cabinet just sound better. Describing their sound is not easy, but here goes; they provide tighter bass, are overall, more “defined” than the other speakers, have clearer highs, have tighter, more focused distorted tones, and they add an overall tone that has been described by others as being "transparent" or “3D”, and with which, I agree.
To my ear, while the Golds are clearly my first choice and are worth the extra expense, the most interesting bit was that among all these speaker options, the stock Mesa speakers came in as my second choice!