I like RS-485 - RS-232 is not particularly electrically robust - I have a hard time calling it reliable except in ideal conditions. +12V single ended, is still 12V single ended. Ethernet is a pretty good sweet spot of robustness, speed, and cost I think (PoE is nice as well) - and I've ended up using it for a number of industrial asynchronous data communication systems throughout the years. Also: It is so ubiquitous that installation and test equipment is readily available (that moreover can be used by technicians) when things inevitably go wrong.
