I have 2 15" l7's and they hit very hard, but the sq is just so so. They also require alot of power, but mine are in a sealed box. The 12's would sound alot better and still hit hard. I wish I would of got 4 12's instead. I think that the l7's would hit harded and the alpines would sound better. The l7's would sound good too.
For all around I would go with the Alpine's, you will get way better sq, and still maintain spl. Not to mintion not minny people have herd of Alpine type X subs.