From purely a $-per-square-inch perspective, the #3 is the hands-down winner over the ST 1400 or 1460. For roughly the same money, you'll be able to buy a smoker with much more "Q-Estate," and some accessories to boot! Plus, the SI has a 1-year longer warranty. The construction of these units is virtually identical, so the price difference is only for the "name" of ST! Been around a little longer, and have inflated their prices to match, but have been kind of stagnant in innovation. Steve, at SI, is trying to stay ahead of the competition. His smokers boast bigger wheels, longer cords, and now have standard handles on the #2 and 3! More things around the corner, but that's the difference for now.
Buy the #3 - as Brian said, you won't regret it! ;D