My wife has a Kindle Fire and a Nook Color. She needed some books from each for here work, and was replacing physical books that were damaged in a flood.
For reading only, I'd get one of the readers (cheaper ones) as the battery life is better.
The Fire is faster than the Nook Color (though I hear there is a newer version). We have Amazon Prime membership (one reason for getting the fire) and she can watch a show for free through the membership. Of course you need Wi-Fi, but we have found this handy traveling with the kids, when staying in Hotels, etc.
IF I was going to do it over at this point, I'd get an I-pad, but that wasn't what whe wanted at the time, and I will say I like the compact size of the Nook and Fire somewhat.
But for reading books only, go with a cheaper model. And if you need on the road access, get 3g. I'd pay more for the one without ads too, but that's me.