We sailed with Viking and the trip was fantastic. From talking with other people who sailed with Uniworld, it appears that the main differance was in the food. Viking imports 90% of their food from the west and on our cruise, we had an excellent Austraian chef. (Previously employed on Crystal Cruiselines.) On Uniworld and other cruises in Russia, the food is all Russian and I take it not so great for American tastes. One person told me that all the meals were some kind of "mystery" meat smothered in dark salty gravy. This has been a couple of years ago. Hopefully the situation has improved. You won't go wrong with Viking, however.