I have an A4 and Rytm and honestly prefer the sound of the drums you can get out of the A4, especially the hats and kicks. You can even get wild FM drum sounds out of it that give the Machinedrum a run for its money.
I also love having the macro performance page for live tweaking drum sounds, it’s sort of like the CTL-8P machine on the Machinedrum. I wish the Rytm had an option to do that in addition to using the aftertouch pads. Just personal preference but I prefer to tweak drums with knobs to pads and I like being able to tweak the parameters of multiple machines at the same time.
Druma is an essential addon to the A4 in my opinion, as is Kimura Taro’s excellent FM and Mod drum packs.