The small-form-factor boards are similar, but all significantly different. This comparison puts the differences in one place to make them easier to see.
The Pro Mini and Pro Micro of any brand of Arduino compatible board seem to be very popular. But choosing between them can be tough. There seem to be so many, and it is hard to distinguish between them. Here is a comparison on the size and features.
|Pro Mini||ATmega328P||14||6||8||32k||2k||1k||$7 – $10|
|Pro Micro||ATmega32U4||14||5||4||32k||2.5k||1k||$6 – $20|
|Nano||ATmega328P||14||6||8||32k||2k||1k||$12 – $35|
|Micro||ATmega32U4||20||7||12||32k||2.5k||1k||$7 – $25|
The prices given above are a range from the cheapest clone to the most expensive genuine article in January 2014. Used in a development environment, where things are plugged and unplugged, powered up and down, jerked around on cables, the clones don’t hold up as well. Reports show failures from all of them clones or downright forgeries, and all from abuse. There has been no reports of failure in the field of either a clone or an original.
Taken from https://www.arduino-board.com/