  We present several results on comparative complexity for different variants
of OBDD models.
  - We present some results on comparative complexity of classical and quantum
OBDDs. We consider a partial function depending on parameter k such that for
any k > 0 this function is computed by an exact quantum OBDD of width 2 but any
classical OBDD (deterministic or stable bounded error probabilistic) needs
width 2k+1.
  - We consider quantum and classical nondeterminism. We show that quantum
nondeterminism can be more efficient than classical one. In particular, an
explicit function is presented which is computed by a quantum nondeterministic
OBDD with constant width but any classical nondeterministic OBDD for this
function needs non-constant width.
  - We also present new hierarchies on widths of deterministic and
non-deterministic OBDDs. We focus both on small and large widths.
