Originally invented to spare horses dying (literally!) on the steep hills of San Francisco, the city's now-iconic transportation is worth a ride if it's easy - waiting for an hour or more makes the decision harder.
The Powell stop/lines (to Fisherman's Wharf and North Beach, from Union Square) typically have longer lines than the California line which starts at California and Market (Downtown, near the Ferry Building). It is also sometimes possible to catch them at the midway/non-terminal stops where everyone lines up - look for the Cable Car stop signs.
For those interested in learning more, the Cable Car Museum is a great (and free!) option and has no lines at all :)
Website: http://www.sfcablecar.com/
Wikipedia: http://en.wikipedia.org/wiki/San_Francisco_cable_car_system
