I like the active careers that let me go to work with my sims. Best one is probably scientist followed by conservationist. I did enjoy the detective and doctor careers, but outside of their actual work shift, I found there's hardly any 'detective' or 'doctor' actions and interactions they could actually do. Scientists and conservationists, on the other hand, I can find a lot of related gameplay for them to do even when not at work.
But my favourite thing to do is not have any career at all and just make up one for my sim. Not being tied to a schedule or routine, I can focus on crafts, skills or activities that makes sense for each particular sim.