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.
I was a kitchen designer for a while, so take me seriously.
The 45-degree dishwasher next to the sink is a bad idea because when the door is open it will occupy the same space as a person standing at the sink.
As for 18 vs 24, just be aware that with 18s you have less selection and they can be pricey. Not a terrible hassle, because the market for appliances is overwhelmingly vast (at Lowe’s we had something like 3,000 refrigerators in our catalogue when I worked there).
But you (and every other person who will ever own that kitchen) will have less flexibility in choosing dishwashers if you design your space for an 18.