I've owned two Kindles, including the larger DX. An iPad is the way to go, period. Not only is it easier to read on-- page turning and stuff is much easier, as is finding a page you're looking for-- but the iPad is so useful for so many other things! Right now, mine contains approximately 350 books (from Amazon, many of which were free), over 700 hours of lectures on history (which I'm fond of listening to), about four days worth of music (that I can listen to either on headphones or any other speaker system that's either bluetooth-compatible or has a standard jack), about fifty hours of other assorted podcasts, and about twelve hours of video. My iPad's memory (I sprang for the largest) is now just under half full.
The iPad is also the best, easiest-to-use GPS I've ever had (due to its size) though it should be noted that when using the Navigon app on it (as I do) it won't pick up traffic information. In addition I can and often do stream Netflix, watch Weather Channel videocasts, and listen to free music from Pandora or just about any radio station in the world that I might desire to hear. It's also perfectly fine for web-surfing, e-mail, word-processing and online chatting if you have a bluetooth keyboard, and best of all you don't have to change devices to do any of this. (I even write novels on mine.) Yes, it's expensive. But I've never owned such a versatile, easy-to-use device in my life. Some things are _worth_ paying for, in my book. (Hint-- if you buy one the case is _important_. Get one with a built-in stand.)
I'll also note that I rather quickly wore out the page-turn buttons on my Kindles-- they lasted no more than about 300 books apiece before they started to get quirky and difficult to use. You can't wear out a touch-screen. Yes, the e-ink of the Kindle is very slightly easier on the eyes. That, however, along with longer-lasting batteries that in practice don't matter much, is the device's _only_ advantage, and in the dark the backlit iPad beats e-ink all to heck-- there's a setting that allows you to show the letters as white on a black screen that does the trick perfectly.
Even though I continue to follow this forum I post here only very rarely because it's unlikely now that I'll be expeditiing any time soon-- my life-circumstances prevent it for now, though I still hope to someday. So I can't say how the two gadgets compare to an _expediter_, and I admit this freely. However, unless you're very budget sensitive indeed, well... though more costly, the iPad is the vastly superior tool. I can say so from much experience with both.