If you don't ride bikes enough to know what 'gear inches' are, which is likely to mean you have not yourself changed chainrings, cassettes, freewheels or cogs, skip this. The rest... the few... I have thought much and am making some changes on my road bike and fixed gear. Links, and more links.
It's all about efficiency. I am a spinner, not a cranker. I do not bother with a cadence monitor. I know I am cranking too hard and spinning too slow if: my legs hurt early and my speed goes down a few km for doing more work. And if you want to learn to spin smoothly, get a fixed gear: spin badly and get spanked.
On the commuting fixed-gear I had it at 74" (28mm tires, 44 ring, 16 cog), which worked well in Toronto, except for a few hills, and worked well when I stayed on the levée paths and east side of Tokyo. Crossing the city, with its ridiculous number of lights to start off from, and finishing over an hour of that with some hills on the Yamanote side, I am wanting to take it down to 69.5" (28mm tires, 42 ring, 16 cog). The latter is the way it came stock. I rarely get spun-out now, and have brakes if I get spun out with the change. It will be nicer on the hills and lights I cannot avoid. 11.5kg/25lb: not bad for a steel mid-range fixed-gear in a 59cm. Too bad I have just found I need to overhaul the headset... PITA.
On the road bike this is no issue on the flats: you can always find a gear, double or triple. However, I want to climb the irohazaka this year, which means I need low gears, but I do not race in pelotons, which means I do not need the highs.
I bought a triple, which was foolish: heavier, and a wider q-factor/tread, and I never use the big ring. It came as 30/42/50, but I changed the 50 to a 46 and still rarely use it. Fact is with an 11-28 cassette 42/11 is 102.2" and tall enough, outside of a paceline. With the 50 the range is 28.7-128.6"; with the 46, -111.9". Now a modern 'compact double' is still a range better for racing than nimble touring and training; a 34/50, even with my wide 11-28 cassette misses a lot of low end: 32.5-121.6". What to do?
This is the shit!
The Sugino OX801D is devilishly simple: 'compact+' The short version is that it is a double equal to a triple without the big ring, so instead of a q-factor of 165mm, 145mm, which is as narrow as a frame will let. That much narrower is said to be 5-10% more efficient. I have ordered the 44/30, with a 175mm crank (love to try 180mm, but the Japanese don't make that size...). With the 11-28 cassette: 28.7-107" with a better spread of gears in the middle than a modern 'compact double'. If that doesn't have enough wall-climbing ability I'll put a spare 26 ring on it: 24.8-107". Incidentally, she's a steel frame/fork bike, 59cm, and still just 10kg/22lb.
Road bikes and fixed-gears come over-geared. There are two reasons: built for doping racers in pelotons, and bravado. Truth is, if you are cranking hard, you are not efficient: you are slower. It's all about efficiency. You want to go as fast as possible for the least work, money and discomfort.* I have achieved that.
*least work - correct gearing to spin, not crank
least money and discomfort - steel over plastic or aluminum; seat and handlebar bags over panniers and racks; tires neither too thin nor wide