Following are the advantages of ASP.NET.
Web application exists in compiled form on the server so the execution speed is faster as compared to the interpreted scripts.
ASP.NET makes development simpler and easier to maintain with an event-driven, server-side programming model.
Being part of .Framework, it has access to all the features of .Net Framework.
Content and program logic are separated which reduces the inconveniences of program maintenance.
ASP.NET makes for easy deployment. There is no need to register components because the configuration information is built-in.
To develop program logic, a developer can choose to write their code in more than 25 .Net languages including VB.Net, C#, JScript.Net etc.
Introduction of view state helps in maintaining state of the controls automatically between the postbacks events.
ASP.NET offers built-in security features through windows authentication or other authentication methods.
Integrated with ADO.NET.
Built-in caching features.