Personally, I like the Origins route combined with an old school Icewind Dale/Storm of Zehir approach. Let me give an example
Here are all of the choices that you get:
Human (Male/Female, of any class)
Salarian STG specialist (Male, choose a class with some tech)
Asari Huntress (Female, choose a class with some biotics)
Turian Marine (Male/Female, must have some combat)
Drell Assassin (Male, must be either combat or biotic, no tech)
Quarian Mechanist (Male/Female, must be either combat or tech, no biotic)
Batarian Renegade (Male, must be either tech or biotic, no combat)
At the beginning of the game, you get the choice to choose one Origin, or, to play through them all. If you choose one, you get the same normal treatment, and you stay with your choice all game. If you choose all, you customize your characters one at a time, and you play through either of their "Origin" story, which is a bit longer than the one in Origins. It also gives you dialogue choices to make, with a wheel, to determine their personality.
After a set point, they begin to merge, and you choose one of those as your main character. The others become your party. If you only choose the one, those slots are filled in with placeholder characters.
Romances occur with other, non-player characters.