For beginners as well as intermediate makers i prefer Arduino Micro or Leonardo. It is very easy to use like an Arduino UNO or Nano and has the same features of ATmega328P as well as a must-have feature support built-in USB and can use it as a USB host Device or HID device. I also prefer Arduino Nano boards rather than using Arduino UNO boards because of its size only.
For simple and minimal projects i love to use ATtiny 16/84/85 microcontrollers(My own boards) or digispark boards. It is cheaper smaller in size and works with ultra-low power mode.
In the IoT perspective, I prefer ESP8266/ESP32 boards if you want to add wifi/BLE features into your project. The cheapest and the best solution for IoT projects so far. Have large community support and supported by different programming platforms like Arduino IDE, MicroPython, ESP IDF, etc.... Esp32 is a powerful 32-bit microcontroller capable of wrapup any heavy project we think!