I'm pretty sure the mix bus version has a long known bug with the SSL model that distorts in a bad way....not entirely sure of the in's and outs of that though.
Out of the 3 NLS emulations, the EMI channel interests me most.
It's always $99 (or cheaper, like $69 on a sale). If you have VCC, it doesn't bring anything new to the table. I am personally using both VCC and NLS less and less.