I have had a few hundred of them apart for repair.
Sturmey Archer invented them about 120 years ago. The AW is their best and the best of all igh hubs (except for AW hubs made around 1980). The AW has been amazingly durable even when heavily abused or neglected. Most of the others have issues. The SW should never be ridden on. the 7 versions of 3 speed with coaster brake have problems. Since the Sun Race purchase in the late 1990s, they had a big push to redesign with mixed results. Any model with a click suppressor is to be avoided. The Sun-Race-Sturmey Archer hubs were availble with roatator shift linkage or the tradtiional axle rod linkage. Many of the hubs with the various combinations of speeds - shift type - brake options have been discontinued.
Shimano got started with 3 speeds in the 1960s. To get around SA's patents, they made all the parts smaller which should have made them more prone to breaking but the vast majority weren't ridden enough to fail. Plenty of those in bins. Most came on department store bikes which were so bad few were used more than a few times. The newer models are more complicated and need regular repacking, especially if used in rain or snow.
Every newer SRAM (more than 3 speed) I've had apart was trashed and not repairable. The 3x7 3x8 3x9 were popular about 25 years ago. basically 3 speed hubs with a cassette body on the driver.
There are some newer and different designs: Nuvinci CVT and the very expensive Rohloff 14 speed hub (>$1400)
In the late 1960s Sturmey Archer let their patents lapse so they got copied and were sold on Schwinn & Sears bikes. Some are labeled "Austria" or "JC Higgins".
Retro fitting disc brakes to forks and frames that weren't designed for the extra forces isn't good. Especially on the front fork. Some frames have disc caliper mounts but fitting narrow hubs to wider frames is another can o worms. Steel frames can be respaced but not aluminum frames. Some of the newer hubs are available in different OLD widths. All igh hubs have special axles that are specific to that brand/model of hub. Most don't have any extra length to add spacers. The axles have to slot in to the frame to keep from rotating backwards when pedaling in some of the gears. Just adding spacers doesn't work.
