I had a TR-8, then a TR-8S, now a Rytm mk2.
The faders are the killer feature for jamming/live. There is a very straightforward purity to the TR-8 that is just fun. However you are stuck with TR sounds (very good ones, and actually rather flexible) and fixed track assignments. The 8S allows you to put any sound on any track, to set up track trigging to layer sounds, and use insert fx on each track to shape the sound further. You can load samples. You have a basic FM percussion engine.
This is all really good. You can do a lot with the 8S! However, I found myself spending a lot of time in the menus on the tiny screen making kits. It does take time. You can make good sounding stuff. But itās not massively enjoyable as a creative process. The Rytm is much nicer in that regard - especially if you get on with the Elektron UI for sound design / editing.
The ARmk2 also has analogue filters and overdrive and actual sampling/resampling capability - this puts it in a different category to the 8S for me.
The Rytm is the most complete machine, no doubt. But all are good. And if you like 808/909/606 sounds you can see the TR-8 as an 808 or 909 with some performance and QOL upgrades at a really nice price.
The TR-8S is a TR-8 with a feature request list thrown at it. Great box but itās down to whether you gel with separating the kit prep work from the jamming/performing.
I have found the ARmk2 to be the deepest and most enjoyable as a creative tool, but given that you are already using OT and A4, that might not be what you need.