There are a few things you should ask your self before buying a new thermostat.
What functions does my thermostat need to control?
Air Conditioning?
Heating?
Fan?
Humidifier?
How easy is it to use? (Electronic devices have a tendency to be over designed.)
Check the layout of the controls
Is the layout logical?
Are the buttons easy to use?
Does the display light up at night? (For nighttime people)
Is it too complicated? Will I forget in a few months how to use it?
Does it offer a child lockout feature?
Programming
Is it easy to program?
Can I program it in a few key strokes?
How many programs can I have at a time?
Is it easy to recall a program for use?
What are the program override features like?
Where does the thermostat get power from?
From a replaceable battery?
How long will the battery last?
Does the thermostat have a battery monitor?
From the heating system?
Is the power source from my system compatible with the thermostat?
Does it have a battery backup?
How often will you have to replace the backup battery?
Will it tell you when the backup battery needs to be replaced?
The questions above are what a typical homeowner may want to ask themselves when choosing a new thermostat. Keep in mind these are basic questions to provide a guideline in choosing a thermostat to meet your needs. Features will vary from brand to brand and model to model. Not all of the questions above will apply to all programmable thermostats.