  We present here a new approach to determine an accurate variational
wavefunction for general quantum antiferromagnets, completely defined by the
requirement to reproduce the simple and well known spin-wave expansion. By this
wavefunction, it is possible to obtain the correct behavior of the long
distance correlation functions for the one dimensional $S=1/2$ antiferromagnet,
i.e. {\em a system without long range order}. The qualitative difference
between the integer and half integer case is also easily understood with this
variational approach. Finally we present numerical results for the 2D XY model,
showing that the present wavefunction has an overlap $> 0.99 $ to the exact
ground state of the $S=1/2$ model for finite system up to $6 \times 6$
clusters.
