  We examine the stability of classical states with a generic incommensurate
spiral order against quantum fluctuations. Specifically, we focus on the
frustrated spin-1/2 $XY$ and Heisenberg models on the honeycomb lattice with
nearest-neighbor $J_1$ and next-nearest-neighbor $J_2$ antiferromagnetic
couplings. Our variational approach is based on the Jastrow wave functions,
which include quantum correlations on top of classical spin waves. We perform a
systematic optimization of wave vectors and Jastrow pseudo-potentials within
this class of variational states and find that quantum fluctuations favor
collinear states over generic coplanar spirals. The N\'eel state with ${\bf
Q}=(0,0)$ extends its stability well beyond the classical value $J_2/J_1=1/6$.
Most importantly, the collinear states with ${\bf Q}=(0,2\pi/\sqrt{3})$ (and
the two symmetry-related states) are found to be stable in a large regime with
intermediate frustration, while at the classical level they are limited to the
point $J_2/J_1=0.5$. For large frustration, the $120^\circ$ state is stabilized
for finite values of $J_2/J_1$ in both models.
