I am currently redesigning my kitchen in a 1930's Midwestern USA house. The kitchen has a decent floor area but the floor plan is oddly restrictive.
My space next to the sink is such that I can either have a standard 24" dishwasher next to the sink and a slightly weird cabinet adjacent to it, or I could have an 18 inch dishwasher at 45 degrees flanked by two small but reasonably sized cabinet doors (or drawers), although the 45 degree plan would dictate a somewhat shallow custom counter depth on the flanks (like 18-20 inches).
I think I would be more proud of the accomplishment of building the angled design, and I think the ergonomics would be optimal.
But I'm not sure about the smaller dishwasher. I have never used a smaller one. It seems like it would be enough for my small family and still plenty helpful for gatherings.
We are two people and run the dishwasher every 2-3 days, but it's really nice to go lazy and throw a pot or pan in there, along with a few plates. You're not gonna get away with that if you go with the little dishwasher.
Also, you're basically using the same amount of energy and water either way. Probably less for the larger one if you compare them full.