I like to include as much variety as possible - so I rotate around households and include different traits, aspirations, jobs, single sims, married, divorced, some with one kid, some with lots, some with pets, uni students, vampires, spellcasters etc. Some have happy lives, some don't, some sims are good, some are bad.
My aim in my game is to enjoy as much of the content I've bought as possible (I have every pack) so, although I haven't yet used certain things (like mermaids), I intend to get around to it all in my multiple little mini stories.
Some aspects are pretty realistic - I don't use cheats and I don't speed my way through skills or careers - I develop relationships and slowly build up their money. I've never had anyone manage to get rich without winning the lottery and I don't do anything I personally consider cheating - like using the young again potion from the rewards, or steel bladder or anything like that. But then I have stories which aren't realistic, like having an astronaut who is obsessed with finding life 'out there', who is going to discover a new planet and fall in love with an alien (or maybe that's not unrealistic, who knows? lol) or a live-in nanny who looks after vampire toddlers.