I think a balance of metal and plastic is best. At least for me.
My 1/16 King Tiger Henschel:
Plastic turret and upper. VERY easy to modify/paint/etc.
Metal barrel + metal accessories/tools. They look good and proper thickness/size/etc.
Torro metal hull. The inner is all metal + metal suspension (proper torsion bars, etc), while the outer is a tough plastic (easy to paint).
Metal tracks/wheels. Durability.
I get the best of both world. The added weight makes the tank react more like a tank too.