Comic Books. I've played with a Kindle and a Nook and both have cons and pros. What sucks about the Kindle is that you have to either know someone that has one or actually buy one to get your hands on it. My brother got one for Xmas and I opened it up and took it for a test drive before he got it. It was pretty impressive, but the keyboard seemed a little awkward. The speed was fine, as well as the menu system once you figured everything out.
Nook, well I've played with it several times as I go to Barnes and Noble at least once a week. I'm NOT impressed with it so far. Very slow, and hopefully the firmware/software update takes care of that. The color Nav. menu on the bottom is a great idea, but looks a little out of place IMO.
iPad, this is the one I'm getting. As a proclaimed Apple fanboy, I'm not ashamed to admit I like to buy their gadgets. The iPad seems to do everything I'm looking for in one nice piece of hardware. The book reader is what sold it for me because I've also been looking to buy a reader for a while now. The color screen is a nice touch as the backlit screen sounds perfect for reading at night rather than having all the lights on. (This way I don't have to wake the GF when I can't sleep and decide to do some reading) Whether or not this will be good for the eyes....I have no clue. I've heard the backlit screen will cause extra eyestrain, I've heard it will help prevent eyestrain, and I've heard it will cause cancer. (J/K, but what doesn't cause cancer anymore?)
Book Stores...right now according to Wiki, Amazon has 20k books available for purchase, Nook will reportedly have 400k (including many of the free classic books), and not much has been reported about the iBooks store other than they will support .epub format which with proper searching has many,many free sources of books.
I say definitely do the research and try to test drive them all before deciding which one to buy and try to find the best deal on them.