"VS" is an older line. It doesn't perform all that good and it's overall quality are quite crappy (but at least it's a little bit better than the friggin' "CX" trash).
If you need to choose between the "VX" and "VS" exactly, "VX" would be a much MUCH better choice (it's a lot better model than "VS", by all terms).
"VX" line are almost the same as "TX" line in both performance and quality, and "TX"es are very good PSUs, so you really should consider getting "VX", you won't be disappointed at all.
Otherwise (if you can get any other of the Corsair's PSUs), I highly recommend getting at least "TX" (or maybe even "HX"/"AX", if you can really afford them).
Never get any PSUs of these lines: "CX", "GS". They are absolute garbage. Stay away from them as far as possible.
P.S. ....I'll repeat it for the 100-th time on these forums (....sigh...): "GX" line of PSUs is the Cooler Master's product, NOT Corsair's, there is no such thing as"Corsair's GX PSU".