ADO.NET in a Nutshell

The Microsoft SQL Server .NET data provider is recommended for all applications using Microsoft SQL Server 7.0 or later, or Microsoft Data Engine (MSDE) applications.

The Microsoft OLE DB .NET data provider is recommended for applications using Microsoft SQL Server 6.5 and earlier with the OLE DB provider for SQL Server (SQLOLEDB). It is also recommended for applications using Microsoft Access databases. Additionally, it can access any data source that has an OLE DB provider that supports OLE DB interface greater than Version 2.5. However, if a data source-specific provider is available, that is likely to be a preferred solution.

The ODBC .NET data provider can be used for any data source that is accessible through ODBC but doesn't have either a .NET data provider, an OLE DB provider, or a vendor-supplied .NET data provider.