I'm a roleplayer/storyteller.
The sims I make have fully fleshed-out character concepts, and I direct their actions based on the personalities I've ascribed to them. And then I put that plum on my blog (which I sadly haven't updated since November, because I haven't been simming in a while). Yes, this guy would do that. No, as funny as it would be, that girl would not do this.
I even go so far in fleshing out those concepts as to plan their outfits accordingly. This Inappropriate sim doesn't really know how to dress, so her Formal outfit just looks awful (a really trashy-looking dress with her Everyday shoes and hairstyle). This other one is a tomboy who cleans up well, so she needs to look stunning in her Formal and Party outfits. This guy over here isn't terribly sociable, but kinda seems a bit fussy, so he has a decent-looking but not exactly amazing Formal outfit (a fairly drab suit and tie). And so on.
I usually start with a single sim with a combination of traits that help shape the personality I have in mind. Sometimes I just want to try playing with a particular trait or two, and I build a personality around them. I also once made a family of four (well, twice, but it was the same family; a Sims 3 version and a Sims 4 version), with traits that clashed in fun ways.
I like my single sims to date premade townies, and to experience a failure or two in the romantic arena before finding someone who's actually good for them. Some will woohoo with just about anyone, while others are more selective. I really miss the attraction system that Sims 3 had and Sims 4 lacks, because I enjoyed letting my sims decide who they wanted to romance.
I can't seem to get into the legacy style of play, because I put so much into creating very specific characters and telling their stories that at some point I just sort of feel like that sim's story is done. This guy got cheated on by his first girlfriend, but now he's got an awesome wife and, well, I guess he lives happily ever after, now.