There are two good answers for this (plus a lot of personal preferences, see gizmo's comment on religious wars)
For public applications, the standard Major.Minor.Revision.Build works best IMO - public users can easily tell what version of the program they have, and to some degree, how far out of date their version is.
For in house applications, where the users never asked for the application, the deployment is handled by IT, and users will be calling the help desk, I found the Year.Month.Day.Build to work better in a lot of situations. This version number can thus be decoded to provide more useful information to the help desk then the public versioning number scheme.
However at the end of the day I would make one recomendation above all else - use a system you can keep consistent. If there is a system that you can setup/script your compiler to automatically use everytime, use that.
The worst thing that can happen is you releasing binaries with the same version number as the previous ones - I've recently been dealing with automated network error reports (someone elses application), and came to the conclusion that the Year.Month.Day.Build version numbers shown in the core dumps where not even remotely up to date with the application itself (the application itself used a splash screen with the real numbers - which of course where not drawn from the binary as one might assume). The result is I have no way of knowing if crash dumps are coming from a 2 year old binary (what the version number indicates) or a 2 month old binary, and thus no way of getting the right source code (no source control either!)
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