What makes for a good built in dishwasher?

I'm looking at dishwashers online. I can't tell why some are way more expensive than others (even in the same brand at the same store for the same size ) based on the online descriptions. I'm looking for something without a lot of bells and whistles, but has some muscle to it. What are some key words and phrases I should be looking for? What are some key phrases that would tell me its going to be weak and flimsy? We are a family of six, that rarely if ever eats out. This dishwasher will see a lot of heavy use.

Other considerations- we have hard water and no water softener. Is there dishwashers that can take that into account? That would be a bell/whistle that interested me, but not a dealbreaker.