I chose my Nordic Tug 37 after chartering a 42. While the 42 is more spacious, it doesn't actually have any more cabins than the 37/39/40 apart from the second head. The 37 can accommodate a dinghy crane and a ten foot console RIB on the boat deck and has space for water maker down below.
The 37 is plenty comfortable for a cruising couple for months at a time, and can take a few kids/grandkids or another couple that doesn't mind cozying up for modest stints. I took mine up to Alaska for several months last summer with my wife and occasional guests on board and never felt claustrophobic.
The 37 is much easier to one-hand. I have no problem taking it through the Ballard locks by myself. The windage is significantly less. I found this to be a problem with the 42, whose thrusters aren't really sufficient to keep it from drifting sideways in any kind of cross breeze.
The 37 will go quite a bit faster (16–17 kn) and with greater efficiency above hull speed when you need to get somewhere in a hurry. I actually prefer the cozier, side-by-side seating for the skipper and mate in the pilot house to being in the pilot seat with the settee behind in the 42.
Moorage is another big consideration. Forty feet LOA is a big differentiator on that front. We were able to find covered fresh water moorage on Lake Union for our 37 right away. We likely would have waited years to secure the same for a 42.
With that said, I wouldn't want to live aboard a 37 full time. But I'd want something bigger than a 42 for that purpose too. My guess is that coming from a sailboat either will seem quite spacious to you.
The 37 is quite seaworthy, but I have found myself wondering at times with wind against current in places like Clarence Straight or the Straight of Georgia if I wouldn't have been a little more comfortable with some more mass below me. You wouldn't be able to easily retrofit a gyroscopic stabilizer in the 37 like you could a 42, but I gather it's a factory option on the current model 40 (which is essentially the same boat).
The full walk around is a nice feature on the 42 but also one that is more necessary with the additional freeboard and the need to go aft from the pilot house to step on to the dock from a reasonable height.
For either boat, be aware that older models experience significant wave-slap noise in the bow cabin in even the lightest chop, though it is definitely worse in the 37. This can be remedied with expensive fiber glass work (~$20k including lay days) to soften the chines. You should either budget for this or for a divorce lawyer if you are purchasing a used boat that hasn't had it done.
If I were going to go bigger than 40 LOA in a tug-style, semi-displacement boat and had the money, I would probably skip past the NT 42/44 and get an American Tug 485. I got a tour of a fine specimen last summer and loved the layout. The banquette off the galley is an especially nice amenity compared to dining at the settee in either the NT 37 or 42. And the lounge space on the boat deck is superb.
Have fun boat shopping. I hope you find something great!
