I favour Mousasi.
It's funny, because I think Rockhold's style of grappling is one that could cause Mousasi major problems. Heavy ground and pound and top control, smooth transitions, unorthodox attacks, etc. But his inability to reliably hit takedowns is what fucks him.
On the feet, his style of striking is terrible against Mousasi. Kick based southpaw with shitty boxing and no head movement? Mousasi would kill him.