We have a Subaru with manual settings (3 dials) and a Volvo with a thermostat. The Volvo was set the day we bought it and I don't know that we've messed with it since. The Subaru, on the other hand, is always being adjusted.
The Volvo one seems to be smart enough to know when hot or cold (dry) air is needed on the windshield. It's pretty great.