In that size range, my favorites are the RP 40, the Duffy 42 and the CBJ 44. Were I pinned down to one of the three, it would be the Duffy because she'll simply walk away from the other two given equal setups and burn less fuel in the process. BTW, with the exception of the 42 and the 35, I am no fan of Duffy.
Nothing specific. The 42 is unique (to the Duffy lineup) in that all the pieces came together to form the best DE at its size. The 35 isn't as successful as the 42 in that respect but its 'generalist' design makes it (at least) one of the best designs at its size.
Its my opinion that there are better designs out there at every other Duffy size. At 31, I'd favor the South Shore 30 or the Mitchell Cove 32.
Of course, I'm a fan of skeg bottoms but not to the exclusion of every built down though.
I have a 42 Duffy and it is a very capable offshore boat. It handles a head sea really well. At 18kt cruise I think she has a good turn of speed for a boat this size, even when loaded with passengers and gear. It is the best boat I have ever had at running the inlet on a falling tide with a breaking sea. Tracks very true and the big rudders make it very responsive to the helm.
I do dive charters so sit on the anchor every day and it is pretty stable in most conditions. She has a flybridge so it rolls a bit more than the standard deck house model, but it is not a snap roll and never feels tender. Passengers don't complain about the ride or the sit at anchor and I have had many comments on how much they like the boat.
Whoever designed this hull knew something about boats. If something happened to this one I would probably look to get another one just like it, well maybe even bigger with a huge single engine....