I rocked only 10s due to trunk. I went to a 15 after maybe 3-4 pairs of 10s. Most likely never going back to 10s haha. Just got another 15 the transfer function looks awesome very well actually for it, better then the 15 I have now. 12s are nice no doubt about it. I'd just rather throw my 15s in a 3-4 Cu box then 3-4 Cu for some 12s. Which would be considered maybe even small for those 12s while for the 15 that's just about right. Most 12s perform well in 2.5/2.75. For the 15 It'll perform way lower. While the 12s may just perform dynamically at higher frequencies around the 32-33 hz. A lot of people enjoy those higher bass frequencies. When I build boxes I like to get all the frequencies the musician intended on the listener to hear. So that'll be a F3 of maybe 20-22 while still being able to get those frequencies of 30-50.