You can send dataset using XML marshling where as in case of recordset use COM marshling.In case of COM marshling they have some specified data type.so before before sending the record set you have to convert the data type based on the COM marshling.As XML is open system there is no data type conversion.

The points of difference are as follows:

1. ADO.Net dataset can contain data from two or more data sources and relate it in memory. For example you may retrieve emp table from SQL Server 2000 database and salary table from an Excel sheet relate them perform any logical operations and put the integrated data to a new database in SQL server. Whereas ADO recordset will contain records resulting from one query to one data source only.
2. ADO.Net objects are represented using XML so they can travel through networks and firewalls. That is not the case with ADO recordsets which are COM objects.
3. Because of XML representation ADO.Net objects are lightweight as compared to ADO recordsets so application scalability improves. The .net objects can be stored in session variables without much impact on scalability of the application.

The similarities in these two are that both of them can be disconnected (actually ADO.Net follows disconnected architecture while ADO recordsets CAN BE disconnected although many times they are used in a connected manner). Both of them offer sorting filtering and batch updates.

Dataset:-

Data set is the Disconneted data Architecture.

Datareader:-

Datareader is the connected Data Architecture.