Which is based on your GPD needs.
And that is why a higher GPH unit can be worth the extra money because you can run it less HPD to produce the amount of water you need for the coming days.
The problem is often not the cost of the higher output models, its the size.
When I had my boat refit and added the watermaker the shipyard had access to a couple year old takeout watermaker from a much larger boat. It had a large capacity, I do not remember but it was several hundred gallons per day.
The price was right. The size wasn't. The thing was huge. It would have not only required completely redoing the layout of my lazarette, it still would have fit so tight as to make maintenance a nightmare.
I opted for a 160GPD model, and paid more for it, but it actually fits in my lazarette and I still have room to move around and actually perform maintenance.
I have to run my generator approx 6 hours a day on the hook to keep the batteries up. That gives me time to make approz 42 gallons of water, which is in the range of what us two people actually use on the boat. A little make up water from time spent cruising and we're golden for laundry.
BTW, our watermaker is a DC unit. We do not need the generator running but like to run it when we run the watermaker because of the noise of the watermaker, which makes a thumping sound, significantly louder than the generator, which we cant really hear.