Oranges are cool amps. A 1x12 will be about equally as loud, because of common phasing issues with 2x12 amps and the negligble dB increase with the extra 12" in a combo context. In general a 1x12 will sound like it has a harder and more direct midrange and have more speaker interaction and "life". A 2x12 will sound more spread out and have a bit more bass response. I think 1x12's are better for hard rock than 2x12 combos in general. Both can be great, but 1x12 combos win for me - plus I sometimes add extension cabinets in conjunction with the 1x12 combo if desired, so you can cover every base starting with a 1x12 combo foundation.
I also have a Genz Benz 2x12 combo, and I also use a 1x12 combo at gigs occasionally.
It really depends on what the venue holds. If the sound system is nice and there are good on-stage monitors, I either turn my 2x12 down, or I bring a 1x12 and angle it up to me, as it's mic'd to get good crisp tone. This allows me to hear myself more cleanly, obviously less bottom end, but with a monitor mix, it sounds wonderful.
If I need even more projection, I might bring a 2x12 closed back w/ V30s at larger venues with less on stage sound reinforcement so that I can get bigger and chunkier tone at loud volumes where I have no monitor mix, but the gig is loud enough through the mains that I can turn that amp right up.
But either way, they both work really well and with a 2x12 combo, 1x12 combo, and a 2x12 extension cab, I can do almost anything. I also have a vintage beat up fender head in the mail so I will also have a head + 2x12 closed back for some places.
Then again, I have reached a point in my playing and with my band, where I have given up on ever having the 'perfect' sound in any room/gig and I can dial just about anything with any configuration in a pinch.
One time, at a larger stage (buffalo rose in golden, CO) my Lonestar Classic died on me during a gig, so I turned on the Peavey Classic 30 1x12 combo and put the mic on it, and for some reason, it actually sounded more present and full....go freakin' figure.
Rule of thumb, there is no rule of thumb, only what your ears tell you and you have to experiment with different cabs/sounds to find what suits you, but yeah, a 1x12 sounds great on stage. Sometimes, you drive the amp harder to achieve a similar volume, which actually opens that fuller tube saturated midrange out of just about any tube amp better and you tear right into the mix. I like that.
Here here. I just noticed that I didn't elaborate. I'm thinking of CABS (duh). I've got a 2x12 cab and am wondering if it's worth dropping the cash on a 1x12. I really like the G-flex (go figure, I don't play anything remotely "Lynchian") but it's a beast. I just picked up a Tiny Terror in trade and really like the way it sounds through a 1x12 but wonder if it's worth pulling the trigger as I'm trying to get a Telecaster project rolling.
I gotta say though, picking up the Tiny Terror in one hand and that light 1x12 in the other sure would be nice on the back.
Thank you for the responses!!! Anyone else have a preference or use both?