"more important" is tough to answer. What's important to you?
More frequent content will almost always gain more attention than slower content with more polish. If you want to gain readers quickly, finding an art style that lets you work quickly and release content more often is very important!
I'm sure it's possible for the art to be so rushed as to be incomprehensible and terrible, to the point where the extra attention doesn't help........but if it's just kinda rushed, or unpolished? most people honestly read webcomics because they want to laugh or to learn more of the story. The more of those things you give them, the more engaged your readership becomes. If your art is still clear and still conveys the joke or story you wanted to tell, then the fact that perspective is off or the lineart is sketchy won't detract from that, for many readers.
HOWEVER
For Runewriters, I spend an absurd amount of time on each page, because I want it to look and feel a certain way. That's what's important to me. So for Runewriters, the quality is more important! However, if I did the exact same comic and spent half the time on the artwork so that I could update twice a week, my comic would gain readers much more quickly and honestly might be more popular, because people would be getting more story and thus getting more into it.
And I don't mean any of this cynically -- the ability to pare down a comic to the parts that are really adding to it and not worry about the parts that aren't adding anything is ALSO a really admirable artistic skill.
Which is why it's hard to say which one is more important. I have respect for both paths! Speaking as a reader, though, I prefer more frequent content.
Having run both kinds (I did a humour/autobio comic for a few years before RW), I'd say it's definitely tougher to make a weekly humour comic work. Because gag-a-days tend to be less "engaging stories" and more just a quick laugh, getting only one a week feels like eating one single potato chip and then stopping. Not very satisfying.
Look at your comic imagining if you were a reader, and think about whether, if this was all you were getting for a week, would you feel satisfied? Or would you feel like you didn't really get enough? When I thought about this for my autobio comic, I felt like the strips didn't really give enough to last a whole week, so updating at least 2x a week was important to me, and 3x a week was my ideal schedule.