Not sure it IS all about the mike, honestly. The thing about VH is, ideally, the harmonies should sound the SAME as whatever is put into them. Use a great mike, they should sound great, use an average mike, they should sound average, but what I hear with MOST VH units, to be frank, is that the original voice sounds good no matter what mike is used (to a certain extent), but the VH itself is what makes or breaks the harmonies.

If the main voice sounds good, but the harmonies suck, you can't lay that at the feet of the mike choice...