I have a Nook because a family member works for the company which puts it out, and I got it as a gift. It's a hell of a lot better than a KOBO (the ill fated eReader Borders put out right before they declared bankruptcy) You can't get KOBOs fixed to save your life and they don't work properly (my screen just died and the WiFi on it stopped working after only a month and I was told after days of trying to get hold of KOBO that they had discontinued the WiFi feature and I had to through Adobe to get the books, after about 1,000 steps. I never bought an other book from them, and then my screen died.
I was happy to get the Nook. Although, I don't use it a whole lot. I do get some library books on it, but our system doesn't catalog them properly, so you have to go through alphabetical order to find a book. *sigh*
I've never even seen nor used a Kindle in person, so I can't really vote. I just know the NOOK is better than the KOBO.