I have both. The 2x12 is easier to transport, takes up slightly less stage space, can get loud, and is very articulate.
Two 1x15's (which is what I have) are easy to transport, can get louder, can get lower (in frequency), and it very articulate.
If my wife held a gun to my head (again) and made me choose - I would stick with the 15's. But I love the 2x12. (I know, not very helpful). I have to agree with mmbongo - you can make the 15's sound like the 12's, but the 2x12 will not do what two 15's will do.
Two 1x15's (which is what I have) are easy to transport, can get louder, can get lower (in frequency), and it very articulate.
If my wife held a gun to my head (again) and made me choose - I would stick with the 15's. But I love the 2x12. (I know, not very helpful). I have to agree with mmbongo - you can make the 15's sound like the 12's, but the 2x12 will not do what two 15's will do.