DataAdapter:Dataadapter is a disconnected oriented architecture. DataAdapter is like a mediator between DataSet (or) DataTable and database. This dataadapter is used to read the data from database and bind to dataset.DataReader:It is read only format, we can't update records. It is connection oriented, whenever data bind from database that need connection and then connection is disconnected.

DateReader is an forward only and read only cursor type if you are accessing data through DataRead it shows the data on the web form/control but you can not perform the paging feature on that record(because it's forward only type). Reader is best fit to show the Data (where no need to work on data)DataAdapter is not only connect with the Database(through Command object) it provide four types of command (InsertCommand, UpdateCommand, DeleteCommand, SelectCommand), It supports to the disconnected Architecture of .NET show we can populate the records to the DataSet. where as Dataadapter is best fit to work on data.