Well, I believe ESP32 module is very popular recently, because of its dual core processor and integrated WiFi and Bluetooth feature! It is perfect board for IoT application. Of course, it is famous because 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. Its running on clock speed up to 240MHz and one core dedicated to wireless functions, another core reserve for user function. This is MUCH faster than its predecessor, ESP8266. Although it is 3.3V system but with it in Arduino UNO form factor, you should be able to to utilize most of the shields out there.

And not to forget there are many community that support ESP32, example microPython, LUA, and Arduino IDE.  

Features

• ESP32-WROOM-32 in Arduino UNO form factor
• Working Voltage: 3.3V
• DC Input Voltage: 5V - 12V DC
• Wifi: 802.11 b/g/n/e/i (802.11n up to 150 Mbps)
• Bluetooth: v4.2 BR/EDR and BLE specification
• RAM: 520KB
• Flash Memory: 32Mb (4M bytes)
• Power consumption:
  • Max current: 250mA
  • Sleep current: 0.15mA
  • Active without WiFi current: 20mA
• Operating Temperature: -40C > +85C

Packing List

• 1 x WiFi UNO based ESP32 board

Document/Tutorials

• ESP-WROOM-32 Datasheet
• Arduino IDE support: https://github.com/espressif/arduino-esp32
• Doom port to the ESP32: https://github.com/espressif/esp32-doom
• The greatest Arduino UNO in the world - by Fernando Koyanagi Instructable, the steps to setup with Arduino IDE.
• Wemos R32 with Arduino - Startup Guide - by Uncle Yong in Hackster