Molecular orbital theory is more recent than Valence bond
theory. Both theories have their adherents and recently VB theory
has had a renaissance. They both have their strengths. Chemists use
both and mix/match. Some very familiar concepts used every day by
chemists spring originally from VB theory, electronegativity,
hybridisation of atomic orbitals.
MO theory has its advocates, an early triumph was the prediction
of the paramagnetism of O2 whereas valence bond theory predicted O2
to be diamagnetic. One criticism of VB theory is that it starts
from a description of bonds as localised pairs of electrons,
whereas in MO all bonds are potentially delocalised.