two 15" or four 12" subs? your opinion

I have a regular cab 90 C1500. Im going to put teh subs in the bed and port them into the cab. Im not wanting anything outragous.Im planning on having two 8" for the mid-bass and two 5.25" for the rest. Should I go with two 15" subs (which brand would you choose) or four 12" subs (I was thinking the L7 Solo-Baric but what would you go with?)