ADO has the recordset and connected archtecture where as 
ADO.net has disconnected archtecture and DATASET

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.

ADO is a com base library that supports only connected 
data. This means that when we access the data (view, edit 
and update) it is affected in real-time,since the 
connection is being used all the time. ADO uses the objects 
as reference data known as Recordset object. Hence it 
basically gives a single table view of the data. We can 
also join tables to create a new set of records in ADO.ADO 
allows to create only client-side cursors. Using ADO we can 
persist records in XML format and XML integration is not 
possible. 

ADO.NET is a CLR based library that supports disconnected 
recordsets. This means that When we access data, ADO.NET 
makes a copy of the data using XML and holds the connection 
to pull down the data or to make any requested updates as 
long as we need. The best method to follow is 
ADO.NET.ADO.NET uses various objects known as Dataset that 
allow to access data in various methods. Hence it allows to 
store the relational model of the database and helps us to 
access /update the data in each related table individually. 
ADO.NET supports both client-side and server-side cursors. 
Also the cursors are handled as classes in ADO.NET 
providing a way to create efficient applications. Using 
ADO.NET we can manupulate records in XML format. Also 
ADO.NET 2.0 provides Multiple Active ResultSets (MARS) 
which allows to have two datareader on one connection open 
at sametime.

Following are some major differences between both

1.As in classic ADO we had client and server side cursors 
they are no more present in ADO.NET. Note it's a 
disconnected model so they are no more applicable.

2. Locking is not supported due to disconnected model.

3. All data persist in XML as compared to classic ADO where 
data persisted in Binary format also.

4. Ado.net uses Dataset where as Ado uses RecordSet.

5.Ado.Net uses Dataproviders where as classic Ado uses COM 
model.

6.Ado.net can able to works on multiple tables where as Ado 
can works on only on etable.