What is the difference between the E model and the base model?

Nest Thermostat E is actually the more practical version compared to the Nest Learning Thermostat, with a 6-Wire configuration and works with up to 85% of 24 Volt heating and cooling systems in the US. It comes with a Frosted display, a Polycarbonate Ring that has a Ceramic feel and is only available in White color. The Nest Learning Thermostat on the other hand isn't really the base model, rather it is the full-featured model of all the Nest thermostats. It has a 10-wire configuration which makes it work with up to 95% of the 24 Volt heating and cooling systems in the US. It supports up to 3-Stage Heating (W1, W2 & W3) and 2-Stage Cooling (Y1 & Y2), including support for Humidifiers and Dehumidifiers, and Dual Transformer HVAC systems. It also includes a High Resolution display with a Metal polished Ring and comes in a variety of 7 Colors to match your taste. Check out this link to learn more about Nest thermostat specifications: https://support.google.com/googlenest/answer/9230098