With i3, I never found an easy way to swap two windows at different levels of the tree. With awesome or bspwm, I can just mod+drag. Also, automatic tiling in various layouts is nice.
I don't usually have complex layouts, and I really appreciate the stacking from i3, so in that sense i3 wins for me, but I guess if your layouts are more complex, you might appreciate bspwm power in that regard.