[Quoth]

You can use a Kobo with an imaginary email address. Then it's pretty private. Do turn off autosync and all reporting features.

The Kindle needs an email address of a real Amazon account and wants a debit/credit card at setup. A solution is gift voucher for the same marketplace. No bank or location details then needed. The Kindle apps are far worse, on PC or Android they are spyware.

Note Adobe DRM contacts Adobe. So can't use any Retailer or Library using Adobe DRM (Smashwords is DRM free).

Due to GDPR they are legally obliged to have opted out by default.

I use my Kindle (real ereader, not app) to buy an Amazon book, if I can't get it on Smashwords. I select "download to PC and transfer via USB". Then use Calibre with a plug in to remove DRM (if there is any, some don't) using the Kindle's serial number (which can copy/pasted from your content management page on Amazon.).

Also you can't so easily create collections on a Kindle from Calibre and not at all if it's not registered.

So I read EVERYTHING on the Kobo. It's also best for annotations via Calibre and Kobo Utilities.
I keep WiFi off except if doing a lookup in a book (Kindle or Kobo). Web pages are ghastly on ereaders.

Madness downloading on the device. I download on my Linux laptop. Often the PD ebooks need cleaned up (Calibre can do this in most cases. In extreme cases I export RTF, read that into LibreOffice Writer, fix styles etc, save archive as .odt and "save as" .docx to import back to Calibre. Then convert to epub.

Also I like to have backups.

The Kobo Touch N905C, Aura H2O original and Libra H2O I have all just work. I use epub2 rather than kepub. I have no need to patch or use KOreader (though you can), though there are some small irritating "features" and maybe one bug.

I have other ereaders for testing ebooks we create and sell. I've also read review of most. The Kobo Libra H2O seems good value and Kobo better than other brands. I have two sorts of Kindle for testing and also to buy books only on Amazon.
I do have a lot from gutenberg.
The ones on Archive.org are often unproofed OCR, so I now often download the PDF (Forma would be better, but Libra far better than Paperwhite or original H2O). If the margins or background is bad I use GIMP, to resize/import PDF, export as mng, (motion PNG, each frame is a page, reverse order), (ImageMagick not safe to read PDFs) process mng into a PDF with trimming, brightness, contrast, bitdepth using ImageMagick. Even that you have to edit the permission settings (for PDF write, don't enable read!).