I think both are bad choices.
I would use a session 0 to establish my expectations as a DM of the group:
-What kind of behavior I expect of them (don't be a chaos agent)
-What theme and style the campaign will be in, and thus what sort of characters would fit that
-That I expect them to work together as a group
-That they are expected to play as 'the heroes', and not go on a random killing spree
Note that this is different from "a DM telling his players how to play".
No, it's exactly telling players how - and what - to play.
The first and fourth clauses above almost mandate characters to be non-chaotic and non-evil; the third clause implies they're expected to be lawful - leaving LG and LN (and maybe N and NG) as the only playable alignments in your game. And the third clause also directly tells them how to play - they have to work together, no independence, no rash actions.
I'm telling them what kind of campaign I want to run
Nothing wrong with that, but that doesn't mean you'll get what you want.
You design (or choose, if using something pre-fab) the setting etc. and maybe set up some sort of story...but the players, through their PCs, in theory then have the agency to run roughshod over all of it should they so choose. If the adventure hooks don't catch their interest they might flip off your story (with or without even realizing it) and go murderhobo orc-hunting in the southern hills. I see hitting these curveballs and adapting to them as simply part of the DM's job.
Most players IME more or less go along with what the DM has in mind, but not all will, or not all the time; and that's fair enough.
and I'm making sure they are okay with that. If that is not how they want to play the campaign, then maybe I need to run a different campaign with them. But I make sure that we're all in agreement before we actually start playing.
I'll get agreement on rules system, and pretty much stop there. After that, I design the setting for them to bash around in and - if needed - I'll lob in some story hooks and plotlines to go with it.
During a campaign, once in a while I'll go a bit meta as DM and say something like "Hey, I've just picked up this new module - it looks really cool and I'd like to give it a run out. First, have any of you been through it before; and second, do you mind if I run it as the next adventure?" It's rarely if ever they'll say no to this, unless it's something they've already played through at some other time.
Lanefan