If you have a good niche I like micro sites much better. They are both good methods, I just find that I do a lot better with good micro sites that have a keyword domain with great content.
But I have only just messed around with autoblogs, I just don't like them. That's just my personal preference. I would much rather have hundreds of original micro sites that will not get banned, then hundreds of auto blogs that can all be taken out by google if they don't like them anymore.