In this article we test three kinds of trial wave functions for the calculation of vibrational excited states of molecules using quantum Monte Carlo. We begin our study with the basis set originally used by Bernu and co-workers and further modified by Acioli and Soares Neto. The second set tested was the simplified Morse oscillator-like with harmonic coupling (SMOL-HC) proposed by Brown to study the vibrational spectra of C-3. Finally we proposed a third basis set, based on the previous two. This basis set keeps the anharmonicity of the SMOL-HC basis but with well conditioned Hamiltonian and overlap matrices. The calculations were performed in the H-2, H-3(+), and H2O molecules. The results indicate that the basis sets proposed in this work yield more accurate results with a smaller number of basis functions.