Repetier Firmware
This is also one of the old hands and was the first firmware to feature an online tool for easy configuration of settings.
I recommend this firmware to all 3D printing enthusiasts who have little to no programming knowledge and want to use 8-bit (Arduino Mega 2650), 32-bit (Arduino Due) or compatible hardware with both processors. The big advantage of this firmware is the online configuration, which allows you to easily and clearly enter the values with explanations in the form and then simply download and install them via the Arduino IDE. For updates, you can simply upload Configuration.h, adjust the desired settings, and download the modified file. It couldn't be easier.
The firmware works very well in combination with an Arduino Mega 2650 with Ramps 1.4 and the Smart Full Graphic Smart Display in combination with the Repetier-Host, you can easily make changes to the firmware on the display (please note that the changes should still be saved manually in Configuration.h, as you can only read/change the settings via the display).
If you control the printer via the Repetier Host, all print information can be transferred to the display, and the settings (pause, cancel, speed, flow) can be adjusted both via the PC and via the display.
{Important note! The Repetier firmware has not been further developed for several years now, so I can no longer recommend this firmware. Nevertheless, I will post my notes on optimization online in case anyone still wants to try this simple but very powerful firmware.}