Manual - Conventional dial or lever style of mechanical thermostat. It doesn’t have many features.
Digital - This has a display screen and is often capable of a variety of useful functions.

The number of terminals on the thermostat that can be used to individually control separate heating functions. Many furnaces that are called two stage heaters will require at least a two stage thermostat to operate appropriately. You may also choose a multiple stage thermostat when pairing different heating equipment. Such as a heat pump and a furnace.

The number of terminals on the thermostat that can be used to individually control separate cooling functions. Some of the higher efficiency air conditioners and heat pumps are designed to use multiple stages of cooling.

Indicates if the thermostat operates electrically on batteries or power from the furnace/air handler.

This feature allows the thermostat to automatically switch from heating to cooling based on the temperature inside. This is useful between seasons when heating may be needed at night, and cooling during the day.