"Sequential is the way to go. Serial would be even better. "
That would be true in order of magnitude dilutions, as in 0.1, 0.01, 0.001, etc. For smaller intervals, you use pipets of appropriate size for each dilution.
In sequential dilutions, errors are propagated and compounded along the series. A serious error in the first or second will result in error in all the following dilutions.
In single-step dilutions, you compound two errors for each one. In sequences, it's two for the first dilution, four for the second, six for the third, and so on. With typical errors of, say, 0.2%, the error in the final dilution can be quite large.