I was in a discussion with the kids over the weekend over who had spent the most time in space. Astronaut Peggy Whitson broke a number of records for Team USA late last year but interestingly the board is stacked with Soviets, then Russians who comprise 90% of the top-10 and 80% of the top-50 given they have operated space stations since 1971 (starting with Salyut-1).
That discussion turned into a quick Top-10 chart.
Note: M1-M6 represents separate mission flight times. The Soviet Union flag has been used for those cosmonauts who were accepted into the space program prior to 1991.