What are the better e-readers to buy and use?
I'd just use an Android tablet or an iPad -unless- you are going to be reading a lot outdoors / in a very brightly lit room, as their glossy screens reflect a lot of light. A tablet's versatility is generally worth the extra cost, and you can read what's online as well as what's saved to your reader.
Amazon Kindle Paperwhite is the best as its battery runs for 1 month on average usage and is better for eyes.
Also,have a look at the best e readers in the below article -
It depends on your main uses and where you would use the e-reader. Kindle Paperwhite is great for daylight/sunlight conditions and even night/dark conditions without any worry of glare. You can read content as if it were on plain white paper, but there aren't many extras, such as apps to download in order to play games. Otherwise, the Nook or Kindle branded e-readers/tablets are good for books as well as games and basic web browsing.
Amazon Kindle range of e-readers. Choose as per your budget.