We had a 23.5 before we got our Seaward 25. They are totally different animals other than the fact that they can both be towed. The Hunter was "exciting" the Seaward a little more boring to sail, you could say. That's in a good way in that it is way more stable and has more room for cruising than the Hunter did. We have had our Seaward out in conditions we would never have left the dock in with the Hunter (and we did sail that one in conditions we probably shouldn't have). Fit and finish and quality of materials is better on the Seaward.
Concerning weights. Don't believe the posted weights. You can figure about 6000-6500 lbs towing weight for the Seaward when you're packed up for cruising. The Hunter is, and feels like a much lighter boat.
You mentioned the inboard on the Seaward. Yes, much less likely to come out of the water. The 1gm10 diesel is a great little motor. If you are in an area with lots of current, you might want to look for one with the 2 cyl diesel, but the single cylinder is not a deal killer. We've had ours up in Maine and Rhode Island, so you just have to time the currents and be aware of your limitations when you have to motor.
The head. Yes, the marine head on the Seaward is a step up from the porta pottie that hides under v-birth on the Hunter. Don't expect miracles in that regard, though. Ours came with a 10 gal holding tank, which is just big enough to keep 2 adults stressed out over where they will find the next pumpout. I did a lot of work to ours including replacing the hoses and pump on the jabsco head. I also experienced many of the "fun" problems you can have with a marine head including, but not limited to, the geyser effect when your vent clogs, you continue pumping, then open the pumpout fitting to pump it out. We ended up replacing it with a composting head and have been happy ever since. So when looking, don't just pass one by cause it has an MSD porta pottie plumbed to a pumpout, or a composting head. It is nice to have an enclosed head.
If you do go Seaward shopping, inspect the arch area closely. These boats don't have a compression post, and some of them had arch compression issues. This is fixable, though. Anything from 1996 and newer had less issues in this regard. That said, don't expect you can get your shrouds super tight on one of these boats (you can't without damaging the boat). It doesn't matter, as they cruise fine the way they were designed. In 1996, the cabin was raised some so the newer boats have a couple more inches of headroom.
Sailing. Our Hunter sailed better than our Seaward when we first got it. There was a bit of a learning curve, I guess. In fact, we were a little disappointed. The shallow wing keel took a little getting used to when sailing up wind. What we found the fix was turned out to be the sails. Once we had a new custom set made, the boat sailed like a different boat. It would likely outsail the Hunter and definitely works much better as a small cruiser for 2 people than the Hunter ever could be. We really liked our Hunter when we had it, and it was a great boat to learn on. The Seaward is just a nice step up.
Mast raising was easier and quicker on the Hunter. Seaward used several setups over the years. Ours works fine, but I've often felt it could use some improvement. It does the job, however, and I've never been bored enough to take that project on.
That's all I've got for you. Dragged this on long enough.