I always thought it was "you-no-vah" :P
Tbh I think it's just a matter of preference. For example, one of the commentators on the VGC World Championships pronounced Ferrothorn "fer-AH-thorn", but the general consensus is that it's pronounced "fer-OH-thorn". Or how, unlike most people, I say "JEN-jar" instead of "GEN-gar", and still others say "GEN-gr". It's up to the individual.