I haven't tried Symphony of Voices, Austin. EWQLSC is certainly the highest-end and most ambitious choir right now, and unless you're expecting it to be as close to the real thing as EWQLSO is, it's hard to imagine that anyone would regret buying it.
Giovani is a children's choir only and is by design a very specific library, but it's capable of producing some nice sounds if you put in the work to make it sound good.
To tell you the truth, I still love the mixed choir in the Kurzweil K2500. It's a pad sound rather than an SATB choir, and in that sense it's primitive since it's a mixed choir that you play rather than program. You won't get it to play choral music, but it's a gorgeous sound.
And if I were in a position to know whether it's worth waiting for the VSL choir, I wouldn't be allowed to tell you. [:)] (I'm not in that position.)