Personally, I have family members with the Kindle, Nook, and Sony, and after having a chance to try all three, I opted for the PRS-650.
I found that the WiFi wasn't that big of deal for me, because I greatly prefer shopping for books with my portable Netbook PC, and I have seen threads where several Kindle owners chimed in to report that they also preferred to shop from a PC and just have the books delivered to the device.
There is still some benefit to the Kindle's WiFi or 3G in this scenario, because the Kindle can be anywhere in the house and will still receive the download the next time it is turned on.
It's not that big of deal though, since you have to hook up the USB port occasionally to charge the device anyway, and I find it convenient to just hook up my Sony while browsing for books with my Netbook, and that let's me both top off the battery and download my books instantly.
I nearly always have my Netbook along with me during any kind of extended travel (including the zip-up case, my Gateway Netbook is only about the size of a hardback book itself).
Even when traveling light with just my Sony and no Netbook, there is no problem because I find that I DON'T NEED TO LOAD BOOKS ON THE ROAD. Why whoud I need to, when I already have about 1250 titles loaded on my Sony at any give time? With 8 to 10 bestsellers checked out free on 3 week loans from my local library, plus tons of free public domain books available on Feedbooks, Manybooks, plus the tons of freebies available from Sony, Kobo, Borers, Google, Bean, etc. I don't lack for reading material.
I actually like the fact that I can carry a complete standalone independent library around with me, that does NOT need access to the Internet.
Personally I would reconsider the Sony, if you can find one at a reasonable price.
But since you seem to have written off the Sony, let me see if I can confuse you even more
Amazon has top notch service, and has always had freebies and other special promotions, but B&N is playing catchup in the ebook market, so they are even hungrier for business, and could potentially have even better promotions and special deals.
Day to day battery life on the Kindle is much better than Nook, but over the long term, the Nook has an easily user replaceable battery. So, if your battery life drops off as the device ages, at least it's easy to fix on the Nook, not so easy on Kindle which must be returned to Amazon (and then I have heard that you don't even get your same Kindle back).
The built in MP3 player on the Kindle is nearly useless for MP3 music playback or standard MP3 formatted audio books, but does at least support Audible's DRM protected audio books Kindle lacks support though for WMA MS DRM as used by Overdrive for many library audio books, so those would have to be converted to MP3 and would be very difficult to manage on Kindle even after conversion. (These converted MP3 audio books work poorly on Kindle due to very poor track positioning controls, which make it very difficult to find your place again if your listening session is inturrupted)
The Sony's and Nook's built in MP3 players work much better for MP3 music and audio book files, but do not work with Audible or Microsoft's DRM protected audio book titles. Library audio books that are available, or can be converted to MP3, will work quite nicely on both the Nook and Sony.
Amazon is a good source, but a SINGLE source. With the Nook or Sony you can also buy mainstream titles from Sony, Kobo, Borders, or Google's Bookstores and anyone else supporting standard Adobe Adept titles.
BOTH the Kindle and Nook get a little cumbersome to manage and slow down with thousands of titles, and are better thought of as convenient readers to carry around a few dozen titles, with a built in book store anex where you can go to get more.
In my opinion, the Sony is better at organizing large numbers of titles and acting like a stand alone personal library (which is why I went with the Sony), but refurbished WiFi Nooks at $99 dollars are also a great value and that would be my second choice.
(No need for 3G Nook, because B&N 3G doesn't work outside the U.S. but If you do decide to go with a Kindle, I would look at the Kindle 3G coverage map and consider going with the Kindle 3G, as this does gives you more options outside the U.S.)