Hey the dual-action video is actually mine!
I may or may not be wearing the red 2(x)ist's at this moment.
pumice - I'll try to answer some of your questions with what knowledge I have on the subjects. In response to your question about Amana and Kenmore: Whirlpool over the years has acquired many brand names. KitchenAid, Maytag, Amana, Estate, Roper, Magic Chef, Jenn-Aire; these are all appliances that are Whirlpool machines down to the core, and simply have a different label on the front, with subtle differences in cosmetics and features. They do not own Sears Kenmore, but are contracted by them to make some of their appliances. The majority of dishwashers and laundry machines are WP built, while recently there are a number of washers and dryers that are built by LG.
Regarding the Whirlpool/Kenmore/Amana top-load washers, they are all mechanically identical, and differ only by their aesthetics and a few features. The Amana-branded models are BOL in that they feature the smaller straight-vane agitator and black speckled basket, and have few, if any, adjustable options, such as whether you can use a deep rinse or if the machine will only spray rinse. The WP and KM machines are more similar, and are the high-end of this platform, with the white porcelain basket and full sized dual action agitator, and also give you more water level and temp options, as well as more cycles, and the ability to choose a traditional deep rinse.
The washer shown in the second video that yogi posted is my WP, a WTW4800 (XQ2 I think? It's too cold to get up and look right now lol), and the video before that is agitatorjamie's, which I believe if not mistaken is the same exact model, but he replaced the dual-action with the straight vane. Myself, I love the dual.
While these washers look very similar at first glance to the previous generation DirectDrives, their drive systems are very different. There is no transmission, but rather a more simple gear box that mainly converts the torque from the drive pulley to power the agitator, and what drives that is a belt-connected motor that actually reverses back and forth to cause oscillation, which is why you hear the whrrrrm-whrrrm-whrrrm-whrrrm sound in the videos. From close observation, it seems that the motor tries to keep the agitation arc at around 180-200 degrees no matter the size of the load, and like yogi said, with lighter loads the motor doesn't need to provide as much torque as would be needed for a heavy load. When time to spin, an actuator switches the "splutch" to lock the tub and agitator gears together, and the motor simply spins them on their way.
Your choice between the Kenmore and Whirlpool models would not be bad either way, as like I said, they're identical. If the triple-action feature is appealing to you, that would be the choice I'd make. In my opinion it seems more of a gimmick, and the KM auger is smaller than WP's, as well as the spiral vanes on the WP being more broad. My specific advice, however: MAKE SURE that the machine you choose has a specific water level selector on the panel, as well as options for the rinses, which will either be labeled as things such as "One rinse w/ fabric softener" or "Deep Rinse", or like mine, "Fabric Softener On". The machines with "auto sensing" and no level selector are anything but effective, and most users complain of torn or stretched clothing because all too often the machines will use water that doesn't even cover the lower agitator vanes for a heavy load. Regarding the rinses, you'll want the model that gives you the above options and to always use the fab. softener option, even if you don't use softener at all, to get a traditional rinse that fills to the level selected.
