What is the best digital home thermostat on the market?

All depends on your budget. Honeywell, Lux, Ritetemp. High price doesn't mean the best.

https://www.toptenreviews.com/home/smart-home/best-programmable-thermostats/

Nest, GoControl, or Honeywell are among the top 3. Nest thermostats are hands down the best in our opinion. Hope this helps, Beth

How easy are they to install?

It depends. The wires that currently connect your thermostat to your furnace have different colors. Each color wire controls a different functions such as On, Off, Heat, Cool, etc. If you have an older 2/3 color wire system, you will not be able to get full functionality out of a newer highly programable thermostat like a Nest. You would need to replace your current wire with a newer 5 color wire and connect it to your furnace correctly. Also, if you change thermostats from an older model (larger) to a newer model (smaller) you may have a hole that does not get completely covered or an area that is a different color/wallpaper that you will have to deal with. Unless you are really intent on the latest and greatest wi-fi type thermostats, check out the brands William suggested and the model that will do what your current thermostat does. Thermostats are basically sold by their programing capabilities like 5 day, 5-2, 5-1-1 for 5 weekdays and 2 individual weekend days and weather or not you have central air operated by the same thermostat. A new thermostat that is the same number of wires that you currently have is easy to replace. Remove the cover of your thermostat and you will see the wires hooked up from the wall and can then figure out what type you need to replace it with. Or, disconnect it altogether and bring it with you to the store. To insure you don't lose any wires in the wall if you disconnect it, wrap them around a pencil that won't pull through the hole.

Ease of Install Beth really relies on the prior installation and your willingness to upgrade it per need.

So, If you have an old furnace with one of the original 2 wire thermostats (rather than 3 wire) your options are Very Limited.

2 wire are best to go with a Honeywell 7 Day Programmable Thermostat (these are compatible with either setup of 2 wire or 3 wire) that costs less than $30 at Home Depor than to go full bloat on a $230 attempt to install a Nest Learning Thermostat (which rarely learn anyhow) that may result taking it back disappointed anyway.

If you already have updated and have the Green 3rd Wire, you can install anything, and as long as you turn off your furnace and follow all of the instructions it'll be a breeze.