The smartest & healthiest dogs are Mutts, because they haven't been over-bred like so many pure-breed dogs who's parents might be closely related to each other. A deep genetic pool provides many benefits.
All dogs have potential health issues and all dogs require maintenance. By low maintenance do you mean does not require a lot of attention and activity, or doesn't require lots of grooming and such? If the former, then frankly you're out of luck because all dogs need lots of activity.