Better to write structure or story first?

For me it depends on what's strongest from the outset. I don't know how ideas come to you, but I've had both "Oh here's this vague idea" and a tsunami of plot points all at once. I think people overemphasize the power that comes from allowing the story to "take its own course" if I've got a fairly detailed idea and it sounds pretty good, I'm not going to jeopardize that for the sake of some misguided desire for spontaneity. On the other hand if I'm confident I can carry through a story without structuring it first, why get in the way of a creative process that may well be valuable to the final product, when I have no better alternatives? So, being flexible works best for me, but that includes the flexibility to be structured and rigid when necessary.

Think of it this way. A structured writer is like sculptor of stone. You better have a good guideline if you want your cuboid to resemble a horse one day. A non structured writer is like a sculptor of clay, you might even bake it until it's no longer malleable one day, but for that you have to be satisfied with the shape it has taken, and until then you can make it into whatever you want.

I like to know what I'm working with, then I make a decision. But that's just me.

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There's no such thing as the establishment. Everyone knows that!

I've seen shows/movies that start off great, and go nowhere. They literally had no idea where they wanted to end up. I look it as having a destination in mind and dancing your way there.

Breaking Bad is a show where they insist they only had one goal in mind, but has been heralded as one of the most well planned programs ever made. According to Vince Gilligan they considered every option for the finale. I doubt it's true that as long as you know where you're going, it'll be fine, but I'm sure it's a lot more likely.

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There's no such thing as the establishment. Everyone knows that!

WEll yeah, if you don't know how to create mini-conflict you're middle act will be a bore. This is where you learn to spice things up with subplots etc.

I love the script for the 1st Total Recall. Every scene is jam packed with mini-conflict that has nothing to do with the overall plot, it's just to keep us engaged.

Not for nothing, I have seen a lot of movies and TV shows get bogged down with unnecessary conflicts that served no other purpose than to make the characters unintentionally annoying. So it's best not to overplay your hand either.

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There's no such thing as the establishment. Everyone knows that!

Conflict doesn't have to be between characters. Writers don't get this. Something as simple as a door being jammed and you having to really yank it open is a micro-moment of conflict. It grabs the viewers attention and stops them from tuning out.

A big complaint about conflict is how children are written as a source of conflict. I've seen so many boards where people say "good movie but the kid wrecked it!"

I wrote a screenplay with a teenage son and a script doctor said to make him and his father estranged and have conflict. I said no way. I'm tired of those worn-out storylines. In my movie him and his son are friends.

Personally I cannot go by a three act structure, if that is the type of structure the OP is possibly meaning.

The problem is, is that I find my characters often motivated to do things that go against that structure, and I have to let the characters do what they got to do, even if means breaking structure traditions.

The three acts are what audiences want but you can have acts within the act.