Vintage integrated Amps. What to look for?

I am sure there are a few that have done what I am thinking of doing and would like to get some opinions on doing so.

I have for years always had separates, and good ones at that. Now while I have always been happy with what I had I have always had the urge to try some vintage gear.
I thinking of selling my separate preamp and amp and getting an old Fisher, Marantz or Sansui integrated amp. I have read allot of good things on the Sansui 20000.

Who has done this and were you happy with the change?? What were or are your likes and dislikes also what vintage integrated amp's did you look at? consider buying or did buy. I would like to have a phono stage on it.

Thanks