I have a Samsung galaxy active tab pro with an S-pen. Samsung's S-pen devices are, as far as I know, the best Android devices for writing (so I think most people who are writing on Android probably use an S-pen/Samsung device)
The only problem with writing on Android, though, is how tedious it is to export my handwritten notes to Amplenote to back them up/make them visible across devices (and it also takes a few button clicks and taps to even start a note). Basically, I can go through the hassle to write on it, but then I have to be sure to export what I write to amplenote, and at that point it's no longer editable, so those notes are hard to maintain, and thus lose most of their value besides as a scratch pad, which I could just use real paper if I wanted.
I don't know exactly what iOS handwriting support is like, because I haven't had a chance to use Amplenote on an apple device/iPad, but anything that lets me write directly in Amplenote on Android would be hugely appreciated (namely for Samsung android since I believe that's the main one people write on, but I'll leave the details to you or other people who have experience with this who want to comment)
I'm sure it's a given, but I also really want the ability to edit/keep writing after a pause, like what seems to be available for iPad now
I often like to write things down when working on things like:
Solving math equations
Mapping out my mental models of programs, systems, or data processing
Writing during meetings, i.e. writing on your device without having to look!
That last one I anticipate having to do/have occasion to do a lot starting a couple months from now, in particular, but is definitely a universal use case now that nobody uses flip phones anymore.
It would be nice I guess if some kind of OCR option were available too, either for real time conversion or post-processing, but since a lot of what I do doesn't involve words (ie I wouldn't want everything to automatically be treated as a word), it would be really helpful if such an option were easily toggleable (though not so easily that I might accidentally toggle it while writing without looking! Though I guess when I'm doing math and such is when I'm most likely to actually be looking at my device, and it's when I'm not looking at it that I'm most likely to be writing words I'd want OCR'd, so I guess if one assumes that while not looking at the device is when one would be most likely to toggle any kind of auto-conversion on, the risk of accidentally toggling such a feature is mainly in accidentally deactivating it, which could certainly be annoying, but not the end of the world, which would be where a post-processing option could also come to the rescue)