  Let $N$ be a complete finite-volume hyperbolic $n$-manifold. An efficient
cycle for $N$ is the limit (in an appropriate measure space) of a sequence of
fundamental cycles whose $\ell^1$-norm converges to the simplicial volume of
$N$. Gromov and Thurston's smearing construction exhibits an explicit efficient
cycle, and Jungreis and Kuessner proved that, in dimension $n\geq 3$, such
cycle actually is the unique efficient cycle for a huge class of finite volume
hyperbolic manifolds, including all the closed ones. In this paper we prove
that, for $n\geq 3$, the class of finite-volume hyperbolic manifolds for which
the uniqueness of the efficient cycle does not hold is exactly the
commensurability class of the figure-8 knot complement (or, equivalently, of
the Gieseking manifold).
