Ahhh what a decision to make. I can speak on behalf of having 2 12's in my car then 3 10's. The 2 12's will play lower louder. The 3 tens will play loud low, but not as loud. Sorry if that's confusing. If you want those 3 10's to hit harder than 2 12's ever will, put them in a well built ported box. Think of it this way, 24 square inches of air being pushed versus 30!!!! I'm in the process of ditching the 2 12's and doing up 3 10's myself!!!
take it from someone who knows
my opinion is pretty much the same. the more diameter on your subs (given comparable specs) the lower it will play. the more overall inches you have (if you can say it that way) the louder it will play.