[Okay, here it goes. More than most readers will want to know, but trying to be helpful to the OP.]
The first decision is whether one wants a mini-tablet type device or a dedicated ereader. There are some very definite pluses and minuses to each, but it is clear from the OP's message that he (she?) is interested in a dedicated ereader.
The next decision is touch screen versus keyboard or just joystick (the cheapest option). I would highly recommend a touch screen. Simply paging forward or back it makes no difference, but for any other operation, a touch screen is so much more convenient.
That narrows it down to two devices, the Kindle Touch vs the Nook Simple Touch. Both are the same price ... sort of.
Amazon does not want you to buy their device without ads. They say that you can do so, but charge you an extra $40. (That is all but saying don't do this.) Most people say what's the difference. The ads never appear when you are actually reading a book and are special offers directed specifically toward you. (You have been looking at reviews on Amazon for your wife's birthday present and they will shoot you an ad that will appear on the device when it sits on the coffee table. Great!)
I confess that I am probably a minority, but my attitude is why put up with this. I have enough spam emails to sort through, see enough billboards driving through town, see all the displays on the scoreboards at the stadiums, etc., why do I want to voluntarily subject myself to more.
Okay, lets get past the ads. When the Kindle Fire came out, it was a set of reviews about the Kindle Touch (released at the same time) that got me interested in updating my ereader. (I had a Kindle II.) It was pretty clear from the reviews that many of my pet peeves about the old device had been eliminated, so I got excited about buying a Kindle Touch. In the end, however, I ended up buying the Nook - certainly partly (mostly?) because of the ads, but because of two reviews that compared the devices side by side and gave a very marginal nod to the Nook.
Pros for the Nook:
When the screen refreshes when you turn a page, the old ereaders turn flash all dark and then display the new page. Some people (my wife, for example) find this extremely annoying. With the Nook Touch this will happen only when you turn the first page and then about every sixth page thereafter. (Not a huge deal in that the page changes are so much faster now days that the annoyance of the black flash is much less than what it used to be.)
Both reviews found the Nook more comfortable to hold. (Again, the difference can't be all that great.)
The Nook has side buttons that allow you to page forward and backward without having to move your fingers and touch the screen. (Not all that it was cracked up to be. The buttons, hidden under the black covering, are hard to push. Not really very useful for a simple page turn. They do become useful if you want to rapid page forward or backwards. Hold the buttons down and the pages flash by.)
Advantage for the Kindle:
As far as I know, any currently released book will be available for both devices at the same price. (Although with the Nook you will have to pay sales tax. I agree with critics that Amazon is gaining an unfair sales advantege here, but still it exists.) Amazon, however, has more "somewhat recent" books available. They went back and digitalized more books that existed prior to when ereaders came out than Barnes and Noble. (Again, mariginal advantage. I have only hit upon one such book that I want to buy and ended it up reading it on my older Kindle.)
The great unknown:
On the whole, I have found the Nook's menu system intuitive and easy to navigate. I hated the menu system on the old Kindle, but would guess that they have something better for their Touch. The one thing that I miss on the Nook is that they do not have a "Back" (undo) option (except for when you are reading an endnote). At times, that would be useful. Ihaven't tried the Kindle Touch menu system so cannot comment on it.
In the end, I prefer the Nook, but think you will be happy with either device.
