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.
If the traffic on this web site is any indicator, the Pro Mini and Pro Micro of any brand receive about 5 times the requests of any other boards. They are very popular. But choosing between them can be tough. There seem to be so many, and it is hard to distingush between them. To help, we've put together two things - a picture of the four boards for comparitive size, and a table with the features of each board.
Although all of the boards have pins 0.6 inch O.C. width, the same width as a 40-pin DIP, the lengths vary with I/O availability.
|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 we found in January 2014. We have used clones and originals of all of the boards above. Used as designed, they all perform equally well. 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. To date we have used 20 to 25 boards, and lost around 5 - all of them clones or downright forgeries, and all from abuse. We have not had a failure in the field of either a clone or an original.