I have worked with these microcontrollers in the past:
- Arduino (Atmega328P)
- NodeMCU (ESP8266)
I’m a fan of the ESP8266; it has WiFi connectivity and so it’s great for MQTT and IoT usages.
The ESPHome libraries are some of the best for connecting microcontroller sensors into your Home Assistant
Random Nerd Tutorials has great diagrams on the pinouts, as the GPIO pins do not align with the PCB labelling. Additionally, some of the pins have specific use cases and can’t be used for external components.