I had all 3 cartridge offerings in the Alaskan until I picked up a Kodiak Backpacker, after which I sold my 44mag Alaskan, as I found the Kodiak to be the better revolver of the two 44mags.
When you compare the Alaskan and the Kodiak backpacker, you're comparing a few different things:
1) Redhawk vs. Super Redhawk Action
2) Redhawk vs. Super Redhawk Gripframe Extension
3) Factory Equipped Grips
4) Potentially 44mag vs. 44mag, OR 44mag vs. 454C or .480R
Ruger Redhawk Kodiak Backpacker 2.75" .44 Remington Magnum
Ruger Super Redhawk Alaskan 2.5" .44 Remington Magnum
Ruger Super Redhawk Alaskan 2.5" .454 Casull or .480 Ruger
1) The Redhawk action is a levered single spring action, whereas the Super Redhawk action is a dual spring design. What does that really mean for the average shooter? Eh, not much. In double action mode, both need a heavy enough hammer spring (mainspring) to give reliable ignition. However, when firing single action, the SRH design can have a lighter break due to the independent trigger return spring. The single spring action can avoid the spring binding and "stacking" feeling to which the dual spring actions are vulnerable. If you don't tune your action and springs, you'd never notice this difference.
The 44mag Redhawk Kodiak Backpacker and 44mag Super Redhawk Alaskan actually use the exact same cylinder assemblies, so there's no difference in action strength between the two.
2) The frame grip extensions are very different between the Redhawk and Super Redhawk. The Redhawk has a traditional exposed frame design, and has a much smaller grip neck than the Super, whereas the Super Redhawk has a "hidden tang" style grip tenon that is fully enclosed by the grips.
3) Coupled with the difference in grip frame design, the Kodiak Backpacker and Alaskan come equipped with markedly different grips. The KB has traditional scales, whereas the Alaskans all come with massive rubberized Hogue grips. Not surprisingly, the Alaskan's rubber grip is nicer for felt recoil.
4) Then you finally get to the cartridge(s) - the Kodiak Backpacker is only available in 44magnum, whereas the Alaskan is available in 44mag, 454c, and 480R. Comparatively, there's not much difference in performance for the 44mag out of either, but the 454C and 480R are much much more powerful in the Alaskan (unavailable in the Kodiak Backpacker Redhawk).