What are important criteria for selecting microcontrollers?

Thinking through system block diagrams for consumer devices, a core component around all software, firmware, and electrical assemblies are built around is the microcontroller (MCU).

How do you go about selecting the MCU?

Searching for microcontrollers can be quite difficult, here’s a useful tool that helps narrow the search dependent on the input criteria entered:

Pinfigurator-Microcontroller Search Tool