I have heard both a few times but never side-by-side... I feel that the 252 is a little faster and a little more detailed in the top end. The 352 is quite smooth and sounds more effortless but the 252 is more "hifi" overall without being cold and analytical. Same applies to the 402 versus the 352 IMO. If it were me, I would get a 252 for sure but it will depend on personal taste and system synergy. I have read that the Duettes are less ruthless than previous Wilsons so the 252 sounds like the better choice there too.
Arthur
Arthur