Meredith Gran of
Octopus Pie rather famously decided to buck the trend and went to a once a month schedule with her updates. Supposedly she was doing very well with the format.
Yet recently she announced she was going back to 3 days a week. (it's the 3rd story down... or 3rd bullet point if you will).
Brad Guigar likes to say updates should be "frequent, consistent and significant to readers."
My own personal mantra, created before I had heard Brad's is "Consistent updates of engaging content."
You'll notice a difference there. I don't include the Frequent.
Personally I believe that engaging content trumps all. That you can overcome just about anything with it. I even believe you can update inconsistently and still be successful if your content is engaging enough.
BUT...
If you want to build a regular audience I think consistency is far more important than frequency. FreakAngels for example is an amazing comic but it only updates once a week. With 6 pages though. And even though I know my comic would wither and die if I only did one comic a week if I updated once a week with 6 comics I'd probably be just fine.
There's a couple things to building that audience though and it's consistent updates and providing value to the visit beyond the comic.
I have movie, game, TV and book reviews. We do a blog. I even highlight other websites. And soon we'll have some animation. And we're launching 2 more comics in addition to the 2 we have already. So I'm offering more to the visitor, and giving them more motivation to return.
But all of this is because I'm trying to build a regular audience so that I can make a business out of this.
If your goal is to use your webcomic as a hobby, creative outlet, soapbox or launching pad you may not want to be as concerned about getting that large, regular readership.
So it all depends on what your intentions are for the project.
For me the webcomic hierarchy goes something like this:
Gag a Day comics > Long Form Comics
Color Comics > Shaded > Black and White
Good Writing > Bad Writing
Consistent Updates > Unpredictable Update Schedule
Great Art > Bad Art
Frequent Updates > Less Frequent Updates
And lastly Great Writing can overcome Bad Art but Great Art cannot overcome Bad Writing.
And I should add that there are exceptions to all those rules but for me that's my recipe for success in webcomics.
So my advice to you is that if you want to get people into the habit of coming to your site then you need to update consistently and the more frequently you update the better. However if you update with a large amount of content you can update less frequently without suffering any ill effects from the fewer updates.
But this depends on what you want from your webcomic. If you don't care about advertising revenue for example... it may not matter to you to get those readers to your site often. Having them check back once a month and maybe make a donation or buy some merch may be enough for you.
Hope that helps.