I know the tutorials on Instructables and YouTube (almost) all use an ESP-01, but I really can't understand why: a real development board is equally cheap (± $2.50) if not cheaper if you count in all the hassle and extra parts you'll need to get an ESP-01 running.
And apart from that, the ESP-01 has very limited I/O available (4 to be exact).
Sure, the ESP-01 can have a nice place inside a specific range of projects once you get to learn how to use it, but is a terrible way to learn (and enjoy) the wonderful world of the ESP8266.