Cost
If you live in Canada, it will cost you C$122.86, plus HST, for the cheapest Kindle. The Kindle Touch and the Kindle Fire are simply not available to Canadians.
By comparison, the Kobo Wifi will cost you $109 (the newer Kindle Touch is $140) . If you are really cheap, you can pick up a refurbished Kobo 1st gen (not wifi) for $70 at Future Shop.
Cost of ebooks
Remember that with a Kindle, you are really stuck buying books from Kindle's store. Many books are not available to Canadians and those that are, are almost always more expensive in Canada. However, when you factor in the sales tax, that American Kindle store does not charge, the Kindle store books are usually about the same price as other ebooks (at Kobo or iBooks, for example).
Library books
Also, keep in mind you can't read library books on a Kindle (at time of writing, that option is limited to some US libraries).
Comparison
If you will spend a significant time with your ereader. Possibly in intimate places like your bed and the bathroom. However, why spend more that you have to.
iOS
-I love my iOS devices (iPhone and iPad) because I can shop for ebooks on many different stores as well as the New Brunswick library. Reading, however, is an other issue. The main problem is that I have the entire freeking Internet at my finger tips. To say there are distractions to reading a book on an iOS device is an understatement. The iPod touch is the lightest reading device and very portable. The iPad is bigger and heavier than an ereader, so less portable, but it is easier to read formatted text like magazines. Anything that had glass will have glare. However, the back-lit iOS devices can become challenging in very bright situations (at the very least, you will have to take off your sunglasses).
-Kobo. Every Kobo feels rushed and imperfect. That is just the way they do things. However, you won't suffer from feature creep. They use the standar ePub, so works with elibrary books and you technically could buy from different stores. I'd advise against the non-wifi model as not having to sink to your computer is a luxury that is worth the extra coin (think buying books while on the can). The advantages of touch are debatable in my opinion. I don't remember doing anything but turning the page while reading books on my iOS devices. Glare is a factor when reading under bright lights or outside. Non-glossy paper wins in that respect.
-Kindle 3G. You can buy an ebook no matter where you are
IN THE ENTIRE WORLD. Even if you are house bound, that might be worth the extra $50. Of course, if you don't have a router, or any intention of getting one (and live within the Telus-Bell coverage area), it is the cheapest option.
-Kindle with keyboard and wifi. If you are realistic, and have access to wifi, you won't spring for 3G. And the keyboard is there if you suddenly get the urge to type something while reading a book. But I've never typed anything while reading a book on my iOS devices.
-Kindle without keyboard or touch capability. This Kindle is Koboesque is its lack of features. But is has wifi. And if you aren't the type to write in the margins of paper books, you don't need a keyboard, virtual or otherwise. The lightest eink reader (but almost twice the weight of an iPod touch).
Need more information? If you really like books, more is never enough: