I've had the best overall experience using an ATTINY85 [1]. It almost serves my purpose for every use case I've had in the past couple of years - Running steppers, basic home automation, wireless, etc.

If you buy them in bulk, you can get it down to less than $1 per MC. [2]

You can even install Arduino libs on it and the Arduino interface has quite good support for it as well.

Some of my projects with it include a DSLR camera slider [3], wireless home automation (turn off lights when I'm not in the room, communicate with my air-conditioner to maintain the room temperature using IR, etc.)

[1] http://www.microchip.com/wwwproducts/en/ATtiny85

[2] https://www.ebay.com/itm/5PCS-ATTINY85-20PU-IC-MCU-8BIT-8KB-...

[3] https://www.instagram.com/p/1AscllHDQ0/?taken-by=discovery.d...