I'm a fan of the late SRAM i3 hubs. If you do the planetary math they should have 12 planets - but 9 are missing! The planets are arranged asymmetrically and the sun, planets and ring gears all have prime numbers of teeth. It has an amazingly simple inside-the-dropouts shift cable. Debuting in 2009 to replace the venerable T3, the i3 is arguably the most 'modern' three-speed design - the AW-NIG/SRF3 dates to 1984, the Nexus to - hmm - mid 90s?, the MBI to early 2000s?
Boo on SRAM department: there are no spares and no support for this hub, and only a single, miserable twist shifter was ever offered. I still don't get why they just discontinued their hubs in 2017 and dropped IGHs instead of selling the tooling and intellectual property rights to somebody.
I have heard/read that the reason that SRAM dropped their line of internally geared hubs is because of the proliferation of people fitting mid-drive electric motors to their bikes and then sending SRAM failed hubs for warranty replacement. I don't know how true that is but, it makes some sense. It is a shame though.
When I was young and car guys were talking about rear end or final drive ratios', I didn't understand until later why they were such odd numbers. Why aren't they 3 to 1. Why are they 3.07? or 3.54? It is so that the gears don't mesh in the same place too often. They have a walking pattern that allows the teeth to wear longer, more evenly and even to survive some damage, if any damage occured in one tooth. I know you know this [MENTION=81459]tcs[/MENTION] , which is why you mention it. I am stating here for others that aren't "in the know" one these details of gearing.