Well, I believe the ESP32 module is very popular recently, because of its dual-core processor and integrated Wi-Fi and Bluetooth feature! It is a perfect board for IoT applications. Of course, it is famous because of the ecosystem built by the huge community. Now programming ESP32 with Arduino IDE is widely used by many IoT developers.
This is the Wemos D1 R32, an ESP32 development board in Arduino Uno form factor. It's running on clock speed up to 240MHz and one core is dedicated to wireless functions, another core reserved for user function. This is MUCH faster than its predecessor, ESP8266. Although it is a 3.3V system, with it in Arduino UNO form factor, you should be able to utilize most of the shields out there.\
And not to forget there are many communities that support ESP32, for example, microPython, LUA, and Arduino IDE.
1 x WiFi UNO based on ESP32 board