  We examine the coherence/incoherence transition temperature of a generic
molecular spin. Our results demonstrates that a molecular spin with a high
coherence/incoherence transition temperature should possess a low spin number
and low axiality, or high spin number and high axiality. Interestingly, the
latter is better protected from the magnetic noises than the former and thus be
the best candidate for a robust electron-based molecular spin qubit/qudit. The
transition temperature can be further optimized if a large non-axial component
of the spin Hamiltonian exists.
