I don't have first hand experience with eReaders with pen digitizers. I've played with some devices owned by friends but I never had a device like that, which is quite odd considering I was a Apple Newton user, then iPAQ, and now my machine is a Surface, so I am all about pen computing. I know that someday I'll get one of those e-ink devices with pen support but I can't really recommend or talk about them besides telling you that they exist and some people really like them. One thing I've noticed is that note taking tends to be available in larger screen sizes. I think that is done so that using the device with fixed-layout media is easier. Most people who are doing annotations are doing it on top of PDF files from what I can tell.

As for smaller devices, I really enjoyed the Kobo Mini, all it missed was a frontlight but it was a device that came out at the same time that those features were moving from premium ereaders into budget ereaders. That device is discontinued (even though mine still works fine) and I recommend small devices for anyone reading fiction, people reading non-fiction, especially technical programming books should be better served with larger devices. Reading wrapped source code in a small device sucks.

I have been looking at a small device from Onyx but from what I have learned here is that Onyx appear to be a GPL violator, so I can't really recommend them even though they make very interesting devices. I think that between them, pockebook and Bouye there is a lot of action happening. Oh and there are multiple Chinese e-ink smartphones in the market, which might be tempting to some people but feels like "too early" for me.

Throughout the years I have used almost every single Kindle device all the way up to the Oasis, Kobo Mini and Forma, Nooks, and Odyssey rebranded devices. From that list you can see that I kinda married my choice of device with having some sort of large bookshop behind it. Kobo is the main competitor for Amazon, Nook had B&N behind it, and the rebranded Odyssey device had a large Brazilian shop backing it. I never owned those independent devices that were not being sold without a book distribution channel bundled with it. That was because I really hate Adobe Digital Editions and will go back to pen and paper before using that crap. Lucky for me many of the books I buy are being sold without DRM so I think that I'll soon be able to enjoy those more advanced and open ereaders in the near future. The Pocketbook Color is the one I'm currently interested in.

I think that the most important factor in chosing an eReader is first figuring out what you want to do with it. If you're buying because you're an avid reader that will consume a ton of fiction, the most important aspect becomes not the device but where you get your books from. In this case I'd recommend a Kobo mostly because I think that Rakuten is a better company for the publishing industry than Amazon and want to see more competition. Kobo devices are as good as Kindles. The only feature from the Oasis that I miss in my Kindle Forma is Audiobook support. Having to go to my phone to listen to my Kobo audiobook sucks.

If you're buying directly from the publishers with non-DRM epubs then you can use anything you like (except the Kindle, you can still use it but it require some hops). In this case it is good to checkout what those independent vendors are selling.

If you're interested in buying your first e-ink device, I'd recommend you pick a cheap entry level offer. Don't go spend a lot in a premium device such as the Oasis or the Forma without actually knowing if such devices are for you. I'm OK paying a ton to have multiple premium devices because not only I fancy myself as an author but because books are an integral part of how I see myself and experience the world. Since my younger years all the way to my current 40s, books have always been a constant source of knowledge and happiness for me, so I can burn some money towards devices that makes such experience better.

Some non-Amazon brands you might want to check out:

* Rakuten Kobo: I consider them Amazon main rivals. I really enjoy "Kobo Writing Life" achievement system which gamifies your reading experience; Overdrive which lets me borrow books from my local libraries; Pocket integration that allows me to send articles from the web to my device. https://kobo.com

* Pocketbook: A major European device maker that just released a quite impressive color e-ink device. Be aware that their site sucks. https://pocketbook.ch/en-ch/catalog/color/color-ch

* Supernote: A device for those that want to take notes. https://supernote.com/

* ReMarkable: Kind of the gold standard in note taking, really. https://remarkable.com/store/remarkable-2

* Bouye: They make nice ereaders. I coudn't find their site but it is easy to find their devices available in online shops. Never used one.

* Sony Digital Paper: Yes, that Sony, they make some kickasss digital notetaking devices. https://www.sony.com/electronics/digital-paper-systems/t/dig... (so does Fujitsu, check them out as well).

* HiSense: is making ereaders and e-ink smartphones.

Barnes & Noble still selling Nooks and Amazon of course has Kindles. Aliexpress has a ton of devices as well, mostly running unlocked Android, but the experience of using such devices might not appeal to you as they tend to be a bit half-baked in terms of UX.