Datatable vs Dataset

One major difference is that DataSets can hold multiple tables and you can define relationships between those tables.

If you are only returning a single result set though I would think a DataTable would be more optimized. I would think there has to be some overhead (granted small) to offer the functionality a DataSet does and keep track of multiple DataTables.

It really depends on the sort of data you're bringing back. Since a DataSet is (in effect) just a collection of DataTable objects, you can return multiple distinct sets of data into a single, and therefore more manageable, object.

Performance-wise, you're more likely to get inefficiency from unoptimized queries than from the "wrong" choice of .NET construct. At least, that's been my experience.