...for the ability to set forward and backward without breaking the mechanism (and Ulysse not needing to be sent back to the manufacturer at the turn of the century for a correction, not sure about Moser)...
...Glashutte, PP 5320 and PP 5236 for ease of viewing...
...JLC and IWC for having the year, decade, century and millennium aperture (even if the century and millennium needs to be manually changed by the manufacturer) which technically means that the dial will never - ever - show the same face on the dial after 24 hours if serviced at the century marks...
...and Andersen Geneve for having the audacity and genius of making a Secular Perpetual Calendar that reads correctly for 400 years via the dial on the back.
There are probably others that should be on my list - this is just off the top of my head.
So much for me to like, but very different criteria. Hard to rank as they each have their strengths.