What works for others, aside from the obvious "just print it lul".
It has no distractions (no mail, messaging, internet, notifications), I can edit stuff with a decently comfortable pen, and it syncs over wifi so I have my notes always with me on my phone if needed. Also the screen is large enough that I read A4 PDFs without zoom or reflow.
I used to print everything and take notes with a fountain pen, now I very rarely do - which is a pity, because I still love my fountain pens.
I have tried printing. But I tend to lose and forget to take stuff. Keeping all papers (and also books) in one place works the best.
It has a large screen. I write with a cheap "stylus".
As per apps, I use "PDF and DJVU Reader", the pro version of Ebookdroid.
I have Mega Sync set up on it and it syncs everything with my work laptop.
I once used a friend's Remarkable. The touch between pen and screen wasn’t smooth enough and gave me an extremely uncomfortable feeling of chalk-screech. I am very sensitive about it, and I use fountain pens on real paper.
Oh, and congratulations on starting your PhD.
Yes, a Remarkable is nice, but something you can trivially send files to is nicer. The iPad lets you annotate PDFs with different apps and pick what works for your needs. It's not a one trick pony.
Notability is also an incredible note-taking app.