Personally I build my levels with almost only models, they are fast,
and you can assign shaders without losing too much speed.
It is possible, with some more effort, and you got all the freedom you want
there are only a few problems in A6:
-no shadows (solvable with a7 and some coding)
-instable collision detection
-problems with bigger levels, no bsp
-slow building if you want to make them in med
-if you don't make them in med, you need an another editor
with blocks all these problems are gone, but
you get new ones back:
-slow rendering
-concave blocks
-less freedom of editing, levels look blocky
if you want to use many shaders, I would say: take the mesh levels, and
use some dynamic shadows and shadow mapping
I hope this helps making a choice....
It really depends on the look and the features you want