Of the three, the Touch is best dressed for success in a highly competitive e-reader market, which also includes devices from Barnes & Noble, Kobo, and Sony.
(I should point out that the Kindle prices quoted above are for the "Special Offers" versions of Amazon's e-readers. In other words, customers get a price cut in exchange for enduring screen ads when the Kindle is idle. The Kindle Touch without Special Offers is $40 more at $139.)
Success in the Middle
The Touch should sell well for several reasons. Its $99 price brings the Kindle into impulse-buy territory. It may become a popular stocking stuffer this holiday season, assuming shoppers can buy a unit in time. Amazon will start shipping the Touch on November 21.
The $79 Kindle may cost less, but I believe the Touch will sell better. The main reason is the latter's multi-touch display, which should prove more intuitive and appealing than the cheaper model's 5-way controller. The Touch is slightly heavier, but only by 1.5 ounces--not enough to matter.