1.ADO used connected data usage, while ADO.net used disconnected data environment.
2. ADO used OLE DB to access data and is COM-based, while ADO.net uses XML as the format for transmitting data to and from your database and web application.
3. In ADO, Record set, is like a single table or query result, while in ADO.net Dataset, can contain multiple tables from any data source.
4. In ADO, it is sometime problematic because firewall prohibits many types of request, while in ADO.net there is no such problem because XML is completely firewall-proof.