OK, I hate to admit it but I have a Kindle Keyboard, an Android tablet and and an iPhone. I am selling my tablet and the Android tablet and saving for an iPad Air.
Anything that gives you the option to flip pages with the swipe or tap of your finger is best, IMHO. On the Kindle Keyboard you have to press the bar on the side of the device which is fine but it soon gets tiresome.
A few times a week I use my iPhone to read my Bible during Bible study. I tap rather than swipe and it works seamlessly. I love it. I have several options to get books through my Kindle app and iBooks. One of these days I will load the library's app or website so I can get audio books. Oh, I almost forgot I recently downloaded Sherlock Holmes Adventures from Old Time Radio which are audio books. We are going to go through those first before purchasing any. On the iPhone I also watch YouTube and my Craftsy classes.
Also, I mostly use the WiFi connection to our home network and skip data charges. A lot of website let you download and listen to things off line. I rarely use data on my phone which also make me happy.
My succession of purchases were Kindle, Android, and then the iPhone. Had I known how much I could do on the Apple phone I certainly would have purchased the iPad Air and skipped the Kindle and Android. AND, my son tried to steer me towards the iPad Air first but I didn't want to spend the money. Oh well! I am happy now.