Subwoofer throw down? Please help?

Ok so I have made up my mind on that I'm getting 1 15" sub or 2 12". Sundown audio sa 12's. 1 SoundQubed HDC3 15", or 1?SoundQubed HDC3 15. No matter what get chosen I Need an amp. I'm going to get the box demetions on davetheboxguy.com. I know they all hit hard I just want to know what one hits the hardest and loudest and flexes my car. It's going to be in my 2004 honda civic.. Please help and thanks for the answers!
My bad and the third one is 1 X-15 D2 - Sundown Audio 15