I pretty much like both songs individually...maybe BH a little more than Shiawase no Tochuu, but damn, in hindsight it seems so obvious now.. like staring you right in the face obvious. And the combination is like both songs squared.
Now I wish each group would make a PV for their song with complementary dance routines that would interlock if performed by both groups together.
@rm the instrumental is still there...it's basically just piano + string sounds.