I like the flats in 1 but not in 3. For my own outfits, my eye likes to see a certain distance (or amount of bare skin) between the pant hem and the top of the shoe. I don't have a formula like Angie, I just know it when I see it, so I experiment with shoes with different vamps (ballet flats, slipper flats, loafers, oxfords...), as well as sometimes with cuffing or rolling the pants, till I like what I see. Heels aren't really going to happen in my daily life, so that isn't really an option: I have them, and they look good with pants, but they won't make it out the door on me.
For your outfits, #1 seems closest to my sweet spot, although I might like it better if the pants were skinnier towards the ankle (kind of an Audrey vibe). In #2 I would roll or cuff the pants or wear shorter ones with those high vamped sandals. Looking more closely at #3: sometimes I will wear a ballet flat with a really long slim pant like that, although usually with some interest, like my leopard flats with my red skinny jeans. I guess I usually look for some edge in the outfit somewhere, so if the flats are "sweet" the rest can't be.