I'm not the person you're replying to, and I've not compared them myself directly, but I've heard a few people describe it as the difference between writing with pen (Supernote) and writing with pencil (RM2). At least on the Supernote side, that matches with my experience - it's fairly smooth, but it does feel like you're writing on paper rather than, say, a glass screen.

There is almost no noticeable lag while writing, and even while doing more complicated things like scrolling through my Kindle list, or resizing a block of writing, the screen keeps up very well.

Purely from my perspective, I find the smaller screen size (roughly A5 dimensions) of my Supernote a lot nicer than the more A4-proportioned Remarkable, but that's just a preference thing - I like writing in smaller notebooks in general. You can also get the Supernote in a size closer to the Remarkable if that's more what you want though.

Having used both the best description would be the Supernote a5x is like writing with a rollerball pen, where the Remarkable is like writing with a pencil.

Both are good, fluid, responsive, but slightly different