Flats need more folding, but otherwise I find them easier to use than prefolds in that you can get a better fit because there are more shape options. I mostly used the oragami fold, and with a pre-mobile baby that might stay on without any fastners under a wool cover or on its own, but once they start wriggling around, you'll need something that closes firmly and holds the diaper on or to start using snappis (I don't like snappis, they snag on things too much).
Flats are easier to clean than prefolds -- they get less detergent/stink buildup because it doesn't get trapped in the layers like with prefolds and fitteds. They dry almost instantaneously. The fabric is nicer. They take a little longer to fold, but they're also the true, original one-size diaper.
Oh, and it's not like flats are a big investment -- cheaper than prefolds.