SparkFun Thing Plus (ESP32)
This is a very powerful board in its own right. It almost seems a shame to use it just for WiFi, though with custom firmware, it could handle WiFi duty and a lot more. The advantage of this board is it has a connector for an external antenna. The board is relatively expensive, but SparkFun has quality products and top notch support. Detailed installation instructions can be found at: https://docs.espressif.com/projects/esp-at/en/latest/Get_Started/index.html 
