I've never been legally married, because if I want to make legal agreements with a person, I want to write them myself, not get the government's package deal that they might change at any time.
But I did have an Outlaw Wedding with my OH. We didn't make absolute promises about the future, because neither of us is comfortable with that. We talked about what we want, what our relationship is like, and what we do in the present to maintain the relationship as one that we will continue to want.
With the OH and also my other committed partners, my main hope (not a promise but an intention) is that we stay in each other's lives for as long as we both live. My main promise to them is that I will talk about conflicts that arise and try to resolve them. I promise that in specific because my tendency is to drift off if there is conflict, rather than talking about it.
I'm finding it hard to answer "what kind of promise would you want from your partner(s)." The way it seems to work for me, in order to interact with someone in a certain way and to hold them in a certain position in my life, I need for both of us to be doing certain things (to show caring and affection regularly, to respect, and to follow through on most agreements we make). If those things don't happen, then the relationship doesn't hold its position.
But I don't want promises to do those things, because promises don't substitute for the actions, and because I don't want someone to do those things if they don't mean them but are only doing it because they promised at some point in the past. I want someone to do those things because that's important to them in the present.