[PaulRyansew]

It would be interesting to analyse various factors: culture, language, genetics (Y/mDna and autosomal), phenotypes etc. I know very little about culture of early Slavs, if one had to treat seriously Marys posts it would be Russians who preserved ancient Slavic habits and style, but whether they preserved or not and whether these habits were Slavic at all is another question, considring low credibility of Burqa it may be unlikely.
I think culture of some eastern-central Slavs may be the closest to the traditional Slavic culture, somewhere around Belarus, south-eastern Poland, maybe western Ukraine (Galicia). These areas had less contact with other cultures i think so (due to geography).