Question is very broad....
See this is where you should thinks on LINQ
1. LINQ to SQL
When the queries and sub queries are more more costlier and has expensive bussines logic in the joins. get the row data to framwork layer and by using LINQ to SQL to the required data. This is the case mostly in Reporting or Reports development.
2. LINQ to Objects
When it comes to implement custom Enumerables and Enumerators it is best to use LINQ to Objects. Because LINQ is developed on these interfaces.
3. LINQ to XML
It is bit strait forward. it is more user frendly then System.XML namspace to read XML data.
Hope this gives good starting point.
Srihari Chinna, Oct 23, 2010
See my previous answer here: http://dofactory.com/topic/1235/linq-to-oracle-provider.aspx
Robert Blixt, Oct 05, 2010