Originally Posted by
schnee
One thing not being covered in this discussion is the way these systems feel in use, and IMO that's an important factor.
So, I'll poke at the usability differences between two extremes - a 1x or 3x system... and how they feel on the ride.
For the 'modern' take, you can run a 1x system - one chainring up front, with 10-12 speeds in the back. Sure, it's simple, easy to maintain, and less to think about, but since it's only 10-12 gears, there will be 'gaps' between them. And, if you are in between gears, you won't have a pleasurable spin - you'll either feel like you're constantly spinning out because it feels too easy, or muscling a too-hard gear. Will this be an issue on your tour? Maybe, maybe not. But it's the option that will be the easiest to get started with and (every few thousand miles, when you get a tune-up) the easiest to maintain. And, it's ideal if your touring is more about short, punchy climbs and descents, like gravel-bike bikepacking.
For the 'classic' take, you can run a 3x system - three chainrings up front, with 9-12 speeds in the back. It means it's a little more fussy with the gearing, since you don't really have 3x the gears, since there's overlap. What it does mean though, is you'll shift the front into the general range of the climb you are doing, then dial it in precisely with the rear. Think of the front shifter as 'modes' - most of the time you'll be in the middle, but you'll downshift into the 'granny' for steep stuff and the 'big gear' when you're on a downhill or on a flat with a strong tailwind. It'll take a bit more effort to get used to, but when you settle in to a long, long climb, you'll be able to get your cadence to a perfect spot - so you're maximally efficient for your effort to speed. This is ideal when your tours include long, long grades - we're talking 30 minutes or so - like on the side of a highway, or mountain pass, created for cars.
There's a lot of flexibility in between these two extremes, but I hope you get the picture.