Help with buying a new Kindle, please?

I'm looking at getting a Kindle. I already own many Kindle books which I now have on my free version of Kindle for iPhone.
The new Kindle with Special Offers--henceforth referred to as KwSO to save typing--is only $114 dollars and is supported by ads at the bottom of the screen. It appears that the only difference between it and the regular new Kindle (for $139) is the ads, but with the cheaper one you get-wait for it--special offers (some decent sounding money savers which I would almost definitely use). Neither of these have 3G wireless, but with the wi-fi, I wouldn't much care. I'm not one to buy on the run when it comes to books, as it were.
For $189, the Kindle 3G + WiFi offers an extra 2/10 of and ounce in weight and a shorter battery life. Um, what? Okay, it also offers free 3G wireless with "global wireless coverage" in 100 countries and territories. (Is that really "global?" Anywho...) Since I don't "buy on the fly," as I mentioned, and the KwSO holds 3,500 books (the same as all of the other versions) this seems unnecessary. Am I missing any functionality that warrants paying the extra $50 to have the 3G other than the "need" to access more than 3,500 books on the go?
Lastly, there's the $379 Kindle DX. The extra $190 gets you a larger screen (which also means 10.2 ounces heavier and 5/100 of an inch thicker), an all around shorter battery life (wireless on or off), automatic screen rotation rather than manual for, I guess, the super-lazy, and... well, that seems to be it. Is the $190 worth, basically, just a larger page? (Especially when that means it will take up more packing space and also weighs in at over a pound, which seems a bit sucky for arthritic wrists such as mine...) Not to me, especially since I am currently unemployed and about to embark on an expensive journey to my undergrad degree.
So. The choice is KwSO for $114, Kindle WiFi for $139 or the Kindle 3G for $189 (currently being offered with a $25 gift certificate).
Have I missed any features?
If you were me, which would you buy?
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UPDATE in repsonse to a question:
There is internet browsing ability on both the wifi and the 3G + wifi versions. So internet browisng on the go for the extra $50, yes. But I have an iPhone on which I do that now and it would be with me anyway.
From Amazon: "Special offers and sponsored screensavers display on the Kindle screensaver and on the bottom of the home screen—they don't interrupt reading. "