Much of this discussion examines the specific solutions to specific, but undescribed, areas. I tend to look at the needs and then find what fits with the least hassle. So far, that hasn't worked. Where I need REALLY low gears, I have a triple. Normally I'm riding a compact, and realizing I don't need it, except when I do.
I'm looking at my usual rides, which generally include a brief stretch of 25% while I'm dead cold and not warmed up. That may include extended stretches of greater than 15% depending on route, or longer climbs of 7% average, reaching 10% for substantial sections. But also include long gentle descents allowing lots of speed. And relatively little flat. But some good long sections of lightly rolling.
Add in a slightly iffy knee that sometimes requires pampering.
There's no "right" solution to that. Warmed up with my knee working well, I'm climbing in a 34/21 and should be on a standard double. Warmed up with my knee acting up and our normal hills, 34/25 will get me up anything. So the compact is useful. Even warmed up and with my knee doing well, the 34/27 is helpful. Anything below that felt too low, not really efficient. But most days I could do just fine on a 39/25 - and I have one old bike set up that way. I used to do the mountains on it without any problem, and I probably still could.
On the top end, my triple rig commuter goes to 52/12 - and I like it. Especially the 42/52. Very very nice. but I hate shifting a triple all the time! I do spin out my 50/12 regularly.
And the compact has the chainline problems. That gap between the rings. It's great when I'm in the up and down territory, but for gently rolling it has me cross chaining constantly, and rarely happy where I am.
I know the cross chaining isn't supposed to hurt, but I tear up chains faster on my compact system than I ever have before.
So I'm mulling over returning to 39/53 with 12/27 and putting my compact on something else. Maybe on eBay! Or just keeping it in reserve.
The triples - I immediately notice the wide Q. Lots of triple riding gradually squeeks a little pain here or there. The double is bad enough! I'd really prefer a very narrow Q.
If I lived on the coast, I'd be considering an 8 speed internal for commuting and a single for regular use, with a cog suite in a saddlebag (I've lived that way before). If I really lived in the mountains, I'd probably be running a triple. If I really lived in lightly rolling terrain I'd be running a standard double, probably 39/53 with 12-23. Living here, who knows what will really work? At least the compact is great for 50% of the time!!!
Commuter. Tandems.