The Johnny Partner is the answer if you are after maximum versatility. It easily dumps in a scat machine if you find yourself by one, and dumps fine with the cone at septic/rv dumps. The hole is just big enough that you dont have to perform "manuevers" with your junk. The lip is fairly short so only those affected worst by taco night can manage to spackle and leave a mess for you. The main downside to it is that it is big. If its just you, the wife and little ones for a weekend on a one boat trip the JP eats up a lot of space in the back of that 14 XT for just a few turds. If you're going to mostly weekend on small trips you might think about some sort of WAG bag system. No dumping required! Im not sure which one is best in that department. When I do wag bags its over a bucket with a seat with gamma lid. Filled bags live in the bucket. If Im thinking more than 12-15 user days, I'll just bring the real shitter.
For a week, or bigger group trips JP for sure. Only problem with the JP on Muti days is that most people dont have them. On trips where multiple tanks are needed, you'll end up with two seats/ unit boxes and or end up using the dreaded eco safe because its still the most prominent. Not a huge deal and Id rather bring 3 extra seats than have to use an eco safe. Of course, with an endless budget, you could buy a few tanks and always be Capt. Feces! Honestly if it keeps you from bringing the kitchen its not a bad thing.
I prefer to shit in and deal with my system (wide open unlined rocket box with seat) over all of them because its the easiest to deal with on the river and gets spackled the least because of the big hole and no lip. Its not the best to clean out though and only DIY options are currently available for RV style dump lids, which is what most people in CO rely on. If your local sewage plant in Gunny will dump and rinse those boxes for you its a good way to go and certainly more budget friendly if you decide you dont want to drop 1k+ on a box to shit in.
The plastic standalone ones, Selway/riverbank/ coyote are fine though a little "tight" and more prone to get spackled than the JP or straight box. I rate them somewhere between the eco safe and the JP.
Whatever you do, dont let anyone convince you that the eco safe is the way to go "because everyone has them". They are terrible to use and if you're doing on the river service, its the worst. I have no idea how people walk away from the mess they make but they do. The right shitter can minimize this problem.
I know you're getting all dialed in but I would imagine you have time to check them all out for yourself. Go on a few trips with different ones or just look at them in a store and think, what's gonna happen to this thing after taco night and tequila. If it seems bad, it'll be worse. The worst offenders run from their mess faster than they can make it.