It does not really matter, as long as you can use the version number to identify your versions (i. e. either add your source control system's internal revision number into the version number) or use it for tagging your releases.
When you do so, you might want to use that number as your third (or fourth) component. It looks confusing if some product jumps from version 1.12345 to 2.12346, but jumping from 1.4.12345 to 2.0.12345 is more common.
About which number to start, I just want to quote Eric S. Raymond:
In the closed-source world, Version
1.0 means "Don't touch this if you're prudent."; in the open-source world
it reads something more like "The
developers are willing to bet their
reputations on this."
