I've got both libraries, and are happy with both, but for different reasons (as has been pointed out). The big feature of VOTA is the stringing together of phonemes to form custom words (usually only half intelligible, but cool nonetheless). SOV has more unique sounds, like a boys choir, Gregorian chants, soloists, and more traditional men and women's articulations and sounds.
However, I disagree with the advice to "wait for the next big thing". There's ALWAYS a next big thing. Get what you need now, use it, and be happy. My advice: if you want a more general-purpose library, it's SOV. If you want to form your own articulations with a cinematic-sounding choir (think big movie scores), then VOTA. Both are fine-sounding libraries.
Or, if you don't mind waiting, that's up to you.