Whichever you can find...
IIRC, Sunset didn't change anything in their version, but fix errata and make it nicer graphics-wise. I just finished playing Operation Star
from my SPI edition... that one and Rostov
are the two best of the bunch.
Stay away from the S&T versions of Kiev & Rostov
as not only do they keep the errata from the original, but they add some of their own.