I voted for 20+...but it depends on a few factors:
With my M&P 45 I usually carry 10 in the pistol and 10 in a spare mag in warmer weather. (A leather single mag pouch on the belt is unobtrusive, looks like a pocket-knife case.) When I wear more layers in colder months, I generally stash magazines in a few pockets, carrying up to 60 rounds. I know if I ever have a self-defense situation that goes to court, this would reflect badly; but I like having the ability to fetch rounds from different pockets if need be.
Just an example - in a New England winter, I might have 10 in the gun + 20 on my belt (using a 2-mag carrier since I can get away with more bulk wearing layers) + 10 in the pocket of my fleece top + 20 in my outer coat pockets.
When I carry the GP100...6 in the cylinder, 6 more in a speed strip, and 12 more in a nice little flat cartridge wallet that mounts on my belt; total of 24 rounds. I just purchased the GP100 this summer, and am debating between speedloaders or more speed strips to stash in my pockets as the months get colder. (I'm leaning towards the speed strips right now.
When I carry the Charter Arms .38 as a backup, I usually just have the 5 rounds in the cylinder. If I carry it as my primary - I keep two speedloaders on my belt (5 each) and a speed strip in my pocket (6) for a total of 21 rounds. Sometimes I'll also load up the cartridge wallet and hang that on my belt in place of, or in addition to, the speedloaders.