As a dedicated drum machine the Rytm is far more streamlined and easier to work with, you have pads, more voices, and more sweet spots as all the machines are tailored specifically for percussion. The A4 is very good at drums and percussion too, and is actually a lot more versatile as it can go outside of the range that the AR allows due to having more parameters to tweak, as opposed to only a few on each machine in the AR. But building a drum sound from scratch takes considerably more time and effort, whereas on the Rytm it’s instant gratification. With the A4 it’s almost necessary to start with presets unless you enjoy a slow and methodical workflow when it comes to making drum kits. Druma, Taro’s FM packs and Drum Enthusiast are all excellent starting points and honestly produce sounds that are on par or even better than the Rytm. Especially when it comes to FM or physically modelled sounds, like realistic snares and toms. The Rytm has samples though, which is a very useful thing to have in a drum machine.