Based on my own experience and what I've seen of other people's comics, I'd say short frequent (and consistent) updates perform the best. I post one page a week. I would post more often if I thought I could do so and still keep a consistent schedule.
Frequent episodes hold the reader's attention better. It's much easier to get back into a story you were reading a few days ago than one you read a month or two ago. They also give the creator more traffic. Every time you post a new episode you get a small boost in new traffic, devoid of weather that episode is one page or forty pages. The more frequent your episodes the more frequent the traffic boosts.
Short episodes are good partly because they allow you to post more often. An episode that's an entire chapter is going to take a lot longer to finish than an episode that's only one or two pages long. Short episodes are also good because they are low commitment for the reader, though. Or at least that's how it is with me personally. I hate to say it, but I always find my self putting off reading comics with long episodes (even when they're really good). I just don't want to dedicate the time when I have so many comics on my reading list.
P.S.
You're right that new readers can be put off if there's not a lot of content available yet. Once you have a few episodes up, it shouldn't be a problem, though. I got around the issue by posting several episodes on the first day, and then sticking to a one episode a week schedule after that.