This is an argument that always comes around. There is not and never has been a society that has achieved "full socialism," in the sense of having zero capitalist institutions and 100% socialist ones. But I think the Nordics (especially Norway and to a lesser extent Finland) are the furthest down the road of democratic socialism. Norway in particular owns almost three quarters of the country's productive assets (that is, wealth excluding owner-occupied housing). Even with the rather restricted definition of socialism as social ownership of the means of production, I think it's hard to argue that owning almost 75% of the means of production is not a socialist thing to do. It also has to be remembered that the welfare state, labor organization, and state wealth ownership in these countries was fought for by democratic socialist parties who won elections and were explicitly working toward socialism. I think it's pretty fair to use the Nordics as a positive example for democratic socialists in the US.