What do i use?

Device

There are many different readers out there, and to be fair, most likely you are already using the one i would reccommend. I have an (very old) Sony E-Reader (2nd Gen i think) and while batterylife is amazing (easily lasts 1year on standby) turning pages, or interacting with it in general is slow and not really useable for me with my current reading speed.  While there is a strong argument to be made for e-ink displays and their benefits in regards to eye-relief, there are other options out there.

The Kindle readers with backlit displays are basically a lovechild of a phone/tablet and a "classic" e-reader. And while i still consider buying a kindle, for me my phone works just as fine.

Granted, having a display thats bigger than a phone is something to be desired for reading, lugging around a second device that does (most likely) not really fit in a "normal" pocket, is not an option.

Bear in mind that i only use a mobile device during lunch-break, on my way to and from my work i use Audible (or Kindle Whispersync) to listen to Audiobooks, since reading a book while driving is not really an option. If i would use public transport, the argument for a reader gets stronger.

I recently caved in and bought a new reader (my Sony is still a backup) and maaaaan having a big display is awesome.
The Reader i chose is the Onyx Note Pro. While i have no real use for the handwriting-options, (since my writing is barely legible on a good day), the Displaysize of 10.3" coupled with a top notch e-ink Display is amazing. I plan on going to Spain for my Holidays, and having a long lasting, comfortable reader is a musthave in that situation.
Considering it runs Android 6, i can use it to listen to audiobooks or browse websites (Royalroad, Literotica, etc.) its basically a tablet, with e-ink.

While at home i exclusively use my PC with the Kindle Desktop app. (Dont even get me started about having a high-end Gaming Rig used mostly for watching Twitch and reading ebooks)

One of the biggest benefits of using the combination of PC/Phone with the Kindle app, is the instant ability to buy/rent books from almost anywhere i go. Additionally, since i only use Kindle and Audible on my phone, with the occasional message on Whatsapp, batterylife isnt really an issue.

It all boils down to convenience, yes, i would prefer a bigger display than my 6 inch phone, but not enough that i consider using 2 devices. And at home even when im reading books, i have an eye on the Twitch-channels and Twitterfeeds i follow, or even the occasional YT-vid in the background.


Slight edit: 
I have recently bought a Kindle more as a way to use it to disable DRM for my PC (which did not work) and i have now started to take it with me more and more, especially if i know i have some time on my hands (Trainride, waiting for something/someone). 
While i still would prefer The onyx or even Sony readers, the convenience of having all my Amazon books available and synched is to good to ignore. 

The main issue here is that i have not yet found a provider which can offer a noteable amount of books in my preferred genres, which would deliver the Books in an .epub format. 
And since Amazon basically disabled all non-Kindle readers with their latest update, kindle is the way of least resistance, at least for now. 

Apps

After having established that i exclusively use Windows and Android as a platform (at the moment), i must say i havent really come across a "better" reader than the Kindle app. While i am not a Fan of their exclusive format, there would be ways around that if you so choose. Since i got Kindle Unlimited i havent really bothered to check other Platforms for eBooks, just because so far, i havent run out of books to read. Especially if you consider the reduced prices for matching Audiobooks and the ability to sync your progress between the two so far for me there hasnt been a better option.

One feature that i would love in a reader is, to be able to sync my Bookmarks and Progress for Websites (Royalroad, Literotica, or similar). Yes it is possible to have my bookmarks syncd between devices, but still it gets tedious to keep up to date, since besides royalroad no platform actually tells me what has been published since my last visit.

I recently reinstalled Calibre as my management-tool to sort, convert and manage my books, It is free to use, and has all the features you could want.