My ideal xmega development board as it's completely application agnostic. It offers access to every pin and has easy to use FTDI access to 5 UARTs, plus 2 SPI and 2 I2C ports. There a no less than 5 ways to power the board, and it can convert anything between 3.6 - 15VDC to either 3.3V or 1.8V to suit the application, and it has some useful UI elements (LEDs and switches) that can be tied into any pin. I love this board and get lots done with it!
This is a board that was created as part of a larger project, a modular power system that provides regulated voltages and manages the LiPo battery. Particularly cool bits are the USB-C integration and the wireless charging. There's a demo of the board in action available, https://www.youtube.com/watch?v=Na4Ped4XoXM
This is modelled PCB for a project that's still in the works at the time of this writing. It's a Raspberry Pi Zero W extension board, compliant with the HAT specification, that adds a host of features to the Pi... more details once the project is actually made public by the client.