I'm going through the same thing right now and here's what I've found and am planning on doing....
First keep in mind that a water maker needs to be either used regularly, flushed with fresh water regularly, or pickled. If you don't, it will get skanked out and shorten the life considerably. It will also make smelly water because the gas from decaying dead plakton passed through the membrane to the fresh water side.
Based on this, you need to think through how you expect to used the boat. If you are a full time live aboard, then regular use is not a problem. But if you leave the boat for weeks at a time (or just don't run the watermaker for weeks at a time), then you will either need to pickle it or flush it with fresh water once a week. But if you have left the boat for a few weeks, how are you going to flush it? There in lies the problem.
The best solution short of pickling, is an automatic self-flushing water maker. These stay awake in a low power mode and count down the days, then perform an automatic flush and start counting down again. I think this is the best solution for non-live aboards. Systems that have automatic flush, all also have automatic operation. You push a button and it runs. A sensor monitors salinity level in the product water and dumps it overboard until the level is acceptable, then diverts it to the tank. When you are done, it stops and does a fresh water flush, then goes into the auto flush cycle. Personally, this is how I want my water maker to work. And the auto flush is essential for the way we use our boat.
This leaves you with 3 choices as I see it:
1) Build your own. If you are hands on, and you don't mind a system that is manually operated and flushed, this is the least expensive way to get water. Lots of people have done it and have no problem operating them.
2) Buy a pre-built system, but one with little or no automation. This is much easier than building your own, but you still need to be ready and able to operate and flush it manually.
3) Buy and automated system.
If you buy a non-automated system, I don't think it matters much whether it's AC or DC powered. Some people have also built engine-driven systems. The choice really has to do with your boat, what systems are available, when you want to run the system, etc. Do keep in mind, however, that the preferred time/place to make water is while underway out in open water. In harbors and at docks the water tends to be cruddy. So think about what your preferred power source is while underway.
If you go for an automated system, look VERY carefully at the power source and how it interacts with the automated flush function. The boat I'm building normally comes with a Village Marine AC-powered system. It has an auto flush function, so I figured all would be fine as long as I'm plugged into dock power when I leave the boat. Not so. It turns out that when power is lost, the auto flush stops and needs to be manually restarted. 240VAC comes and goes on the boat based on generator run time and shore power hookup. And shore power is not reliable. Every blink resets the flush cycle, so in practice it's really a manual system, not automated unless you are on a big boat with 24x7 AC. That's not me.
So I'm going back to a Spectra system which is what I have on my current boat. It's completely automated (even more so than the Village Marine system), and is DC powered so providing it with uninterrupted power comes naturally. And I think DC is a much better way to power a water maker while underway rather than having to run a generator. Also keep in mind that you need to keep the water turned on with an auto flush system.
Lots of people associate DC water makers with low output, and AC with high output. This really isn't the case except at the extremes. The DC system I'm putting in is 1000 GPD which is a lot of water.
By the way, I currently have a 12 GPH system and I wouldn't want one any smaller unless your boat use has you underway for a long time each day. 3-4 hrs replaces our day usage after flushing etc., but to keep up we need to run every day. If we let the tanks get down, it can be a challenge to get them filled back up again. And there are lots of places where you can't/shouldn't run it, so skipping days it quite common.