Imho .. 14 ... Rohloff Hub . it solves the double shifting of all derailleur schemes by having an equal difference between gears and turning the grip pull pull 2 cable shifter, one follows the other..

and you can shift down even when stopped. so very useful when you need to grab a lower gear in the middle of a hill..
or go thru them all till you get to the 2 foot gear, and have a nice walk.

external gear ratio 1:2.4, hub cogs are 13 for small wheel bikes ,

and, 15,16, 17 for 26 & 700c wheel bikes so 36, 38, 41t chain-rings or larger.

Before I got my Rohloff bike I traveled widely with a 6 speed: 14,17,20,24,28,34 on the wheel,
and a 24,38,50 on the cranks 622-40 wheels.

Friction /ratchet bar cons, 80's Campag MTB derailleurs