First, and foremost, they need to be comfortable, whatever other features you are considering. That being said, a Boa closure will help with comfort because it is easy to dial in the tension before, and during a ride. A carbon sole will also be stiffer, and transfer more force to your pedals, but I'm not going to say that you'll be able to tell the difference between a carbon sole, or a composite one. If you walk around a lot, some of the higher end shoes have replaceable rubber pads that wear from walking, but I've always found when they wear out, I'm ready for a new pair of shoes anyway. If you get leather outsoles (instead of a mesh material), they will be easier to clean if they get dirty (they will get dirty).

And lastly, there is an unwritten rule I read that your shoe color needs to match your helmet ;-)