I hate to sound ignorant here, but what two cab combinations generally sound the best? It seems like many here on TB strongly dislike the 4x10 and 1x15 combination.
Additionally (to whoever answers this question), could you explain why this combination, generally speaking, of course, results in better tonal quality than the aforementioned combination?
A 4x10 has nearly twice the speaker area as a 1x15. This means that even given similar sensitivity between the two cabs, the 4x10 will move way more air, and consequently be way louder.
A single 15 usually only has about half the power handling as a 4x10 as well. This means that the 15 will start crapping out when the 4x10 is still going strong.
As well, due to the fact that you can hear the 4x10 better (since it's almost definitely way louder), and that people usually put the 1x15 on the bottom, you could blow out the 15 and not even hear it.
If you're going to mix 10"s and 15"s, it's best to keep the ratio 2:1. Also, I used to put the 2x10 on the bottom and the 15 top when I used a mixed rig.
Still, two identical 15" cabs (or a 2x15), or two identical 4x10 cabs (or an 8x10) will more reliably sound good.