Having never been a player in a weekend game before, I don’t think I can really comment with respect to LARP, but I will comment on my experiences with tabletop.
In tabletop, I definitely prefer a campaign, I think the same reasons that people have mentioned above, such as the greater chance for character development. Personally, I also like that you can have recurring NPCs and locations that your characters will already have experienced in-game (and recurring jokes too). What’s more, I tend to be someone who has to spend a little time working themself into something (e.g. who my character really is, and what they are like), and one-offs generally don’t allow for that, but most campaigns will, assuming the character survives for long enough. Although I do agree with the comment above that a one-off tends to let most people feel more free to do everything and anything, because they’re not so attached to their character.
With regards to LARP, I’d also say that I tend not to be the biggest fan of one-offs, simply because many of them are large social games, and I’m not great with crowds and even worse at en masse socialising, so I tend to be the person who ends up in the corner not doing anything for 3 hours - people who have run big one-offs I’ve played in might remember that I tend to request characters who other characters will have a reason to approach (which worked fairly well for me at the run of Hindenburg last year). Smaller one-offs are a different story though.