Here is a quick post to answer an interesting question from one player on Facebook : "What has been the best selling SGS game so far?"
So, if you consider from the start of the serie, since SGS Winter War, then the four best sellers in term of quantities are : SGS Taipings, SGS Korean War, SGS Afrika Korps and SGS Winter War.
It changes a bit if you consider the fastest selling SGS titles, so in term of time since their release, then it is currently : SGS Taipings, SGS Nato's Nightmare, SGS Korean War and SGS Afrika Korps.
In a way we can say that so far our top 3 would be : SGS Taipings, SGS Korean War and SGS Afrika Korps.