4 door, sunroof, fun to drive

I would highly recommend the Mazda6 or Mazda3. I have a 2014 Mazda3 Grand Touring 5-door and a coworker has a 2016 Mazda6 Touring 4-door. Both meet the requirements fully. They both have great chassis, steering and driving fun. The interior is a class above others as well. I get about 33mpg avg in my 3 and my friend's 6 gets about 29mpg. Both will fit in with your budget too.

A Buick LaCrosse would easily fit those requirements and be a better quality ride than those listed above. Style, comfort, roominess and a 2-3 year old one with a CPO warranty to 100,000 miles would be one of the best options in the luxury segment and give you piece of mind.