Kindle is annoying if you want to move your books around and the author didn't release them without DRM like the awesome Brandon Sanderson does. There used to be a crack using Calibre, but that didn't work last time I tried it, because Amazon keeps changing the format to prevent people from being able to control their own content. It sucks.

I have the Oasis and the form factor is pretty good. Not as good as the older Nook was, but okay. The old Nook had a really good form factor, tactile rubber, and was very lightweight. They released a new Nook a couple of years ago that was pretty close, but it's gone again last time I checked. I had the Kindle Voyager before the Oasis and it's okay. The Paper White is pretty good, but I want physical buttons, and a large edge to hang onto so that I don't accidentally change pages by touching the screen.

The Kindle store is nice because they have pretty much everything, but it's kind of expensive. Recently my Kindle started updating the store every single time I open it, which is very annoying. There doesn't seem to be an option to disable the automatically update.

Text selection on the Kindle is great! I play around with the Nook whenever I go to Barnes and Noble and it's not as good. On the Kindle you can hold one word, then tap another word somewhere else, and it'll highlight everything in-between and the two words you touch.

I've looked into Kobo a couple of times when frustrated that I couldn't move a book to a non-kindle device, but they're pretty expensive. My Oasis was also expensive, but it still works, so I'll probably stick with that until it stops working.

Best of luck! eBooks are awesome and I greatly prefer them to real books now.