How do your sims MOSTLY earn the living?

Honestly, at this point I make more money from selling Lemons, Roses, Apples etc. than from my sim-husband's career. My sims could live off it.

Depends on the Sim/household. Normally either a career, painting, and/or writing, but I’ve recently found out what a useful source of income gardening is since they’ve overhauled it to be less of a hassle. Sometimes I’ll decide to have someone run a retail store and sell things they’ve found or made.

A combination of all the above. It depends on what stage of life they are in. Rarely cheat to give them money though. I'm more apt to take money away than I am to give it to them.

Going to work and through collection duplicates.

There should also be an option for "all of the above." Most of the time my sims will have their career, and then a hobby that makes them money, like gardening, writing, a musical instrument, painting, etc. That's the best way I've found to make money in game if you don't want to cheat. Gear everything towards work in the young adult stage, or maybe even as a teen, and then by the time they are adults they should have a pretty nice nest egg, specially if you get the Wealthy Aspiration reward that gives you weekly investments on your funds. Sometimes, however, I have my insanely rich sims gift large sums of money to their friends or ex-lovers. It all depends upon which sim I'm playing.

Motherlode :D

I don’t have a staple. I have them go for whatever fits their background story.

I send them to work, paint and garden

There's not one of those options that I'd say is specifically their main income. My sims usually only do careers for aspiration goals or just to play the active careers. Income is a combination of most of the hobby activities. I haven't bothered with money cheats in ages, they really just never need it.

Work is their main source of income, with everything else on the side - though, the first few days it's anything goes as they try to afford to furnish their houses! Kind of need an all of the above at any given time option lol.