  We study the problem of optimal preparation of a bipartite entangled state,
which remains entangled the longest time under action of local qubit noises. We
show that for unital noises such a state is always maximally entangled, whereas
for nonunital noises, it is not. We develop a decomposition technique relating
nonunital and unital qubit channels, based on which we find the explicit form
of the ultimately robust state for general local noises. We illustrate our
findings by amplitude damping processes at finite temperature, for which the
ultimately robust state remains entangled up to two times longer than
conventional maximally entangled states.
