I have the Kindle app on my iPad, my Acer A100 tablet, my cell phone, and on my desktop computers (all pcs). I've had a Nook Color which has no capacity to utilize the Kindle app, and I'm looking at purchasing the basic $79 Kindle for a friend's son who's limited to computer access due to a head injury (but can read just fine).
I like the portability of a tablet-sized unit. A 1500-page "bible" weighs the same as a 3-page short story and I can carry around a thousand books in my pocket and they weigh exactly as much as my tablet or cell phone.
If you're looking at reading outside you're going to need an e-ink device as LCD screens suffer fade out from glare in full daylight.
Kindles start at $79 and go up from there to $199 for the Kindle Fire. My iPad ran me $553 out the door at Best Buy. My Nook Color cost $199. My Acer A100 cost $328. A $79 Kindle is very reasonable, very lightweight, and very capable as an e-reader. It is not, however, a tablet device.
Get a device which is expandable with microSD memory or has cloud storage (most Kindles have both), but books are tiny, memory-wise, so you don't have to go whole-hog with some massive 32GB card when a 4, 8, or 16 will be perfectly adequate.