Check out the link I posted.
From what I've been reading, it sounds like the black box Russian is more of a dark over-driven sound, the green box is the most fuzzy, and the US version doesn't sound like any of the Russians.
Your best bet is to try them and see; that is, if you can find a store that has the US and Black Russian models. However, it seems there is a big difference in quality between the US and Russian models. Buyer beware!
Not an endorsement, but there is a seller on eBay that is marketing modified black Russian models that have the cheap components replaced with quality ones. A quick search will find them easily.
Aloha!