For speed of loading firmware, the SWD interface would be quickest, followed by UART, then OTA.
For prototype quantities, the BMD-3xx-EVAL board can be used to program target hardware if the target design has an operating voltage of 3.0V to 3.3V. A standard ARM 2x5 male header on 0.05" centers is implemented. See our BMD-3xx-EVAL user guide for the pin-out.
For production quantities, an external SEGGER J-Link debug probe is recommended. The base model is sufficient.
Another common connection is the Tag-Connect layout in order to reduce the BOM and PCB real-estate. The Tag-Connect cable plugs into the same 10-pin header, but only uses 6 pads on the target hardware:
The "NL" version has the smallest footprint.
For UART, only TX, RX and GND are needed along with external power. This would use the RigDFU bootloader.
A FTDI USB-UART interface is a common method of connecting to the module UART.
Our BMD Software Suite contains scripts in the "bootloader-tools" repository for both UART and SWD programming as well as OTA for field updates. If you don't use our RigDFU bootloader, then any Nordic programming technique can be used. Access to our BMD Software Suite can be requested here.