I'm still learning about these. Till then this page is under construction.
Here I am going to compare 4 boards all available at HobbyKing. My test bench is going to be the Bang Buck Quad.
I have a few tests in mind, but first thing I need to do is get my filming methods worked out. So watch this space.
Lots of firmware available.
Much more sensitive to vibration than the other boards.
Must re-flash or even re-compile to change configuration making a programmer essential.
No external oscillator, if your ESCs have oscillators (most do) you will find that on colder days you will need to re-calibrate the ESC's as wont get full throttle and the board might not even arm.
I'll try and explain why. Think of a hamster in a running wheel controlling the speed of the MCU. With an external crystal the hamster is in a nice temperature controlled room, a nice environment so he can keep a steady speed on the wheel. Using the internal oscillator is like having the hamster and his wheel out in the open. When it gets too hot he slows down and when it gets cooler he speeds up. This difference is quite big, this is from the Atmel datasheet:
this document will tell you if your ESC has an oscillator or not.
i86L has a 16Mhz Crystal and does not have a disarm function which fixes that nasty bug. It is also cheaper.
The KK2 wins hands down. Easy adjustment and setup brilliant user interface and, for those who are in to it, the source code is simply a work of art.
Auto level is not quite there yet but KapteinKuk is working on it. In fact the code is there just not enabled and tested enough yet. Shane Colton enabled this code and made some changes and these hacks make the auto level work really well. I've been flying with the hacked code on a tricopter and it is awesome. Turn it on and it levels out in less than a second. However it is experimental avoid the first version that you might see in KKMultiTool. Here is some information on the second version that I have had some success with.
UPDATE: KapteinKuk has taken a hint from Shane and completely nailed the auto level in v1.5 of the KK2 firmware. Works great.
On a side note KapteinKuk has a great video on PI tuning, just remember to wear brown undies.