ActionResult() is an abstract base class that defines the general result type for MVC actions. ViewResult() is a concrete subclass of ActionResult() that renders a specified view to the response stream. Some key subtypes of ActionResult() include ViewResult(), PartialViewResult(), EmptyResult(), RedirectResult(), and JsonResult(). ActionResult() allows for polymorphism and dynamic behavior by returning different result types from an action. It should be used as the return type when an action may have different behaviors, while ViewResult() can be used when an action will definitely return a view.

1. S.No ActionResult() ViewResult()
1 What is ActionResult() ?
ActionResult() is a general result type that
can have several subtypes.
ActionResult() is an abstract class.
ActionResult() is a base class for
ViewResult()
In MVC framework, it uses ActionResult
class to reference the object our action
method returns. And invokes ExecuteResult
method on it.
What is ViewResult() ?
ViewResult() renders a specifed view to the
response stream.
ViewResult() is a concrete class.
ViewResult() is a derived class of
ActionResult()
ViewResult is an implementation for this
abstract class (ActionResult class). It will try
to find a view page (usually aspx page) in
some predefined
paths(/views/controllername/, /views/shared/,
etc) by the given view name.
2 What are the subtypes of ActionResult
class?
. ViewResult - Renders a specifed view
to the response stream
• PartialViewResult - Renders a
specifed partial view to the response
stream
• EmptyResult - An empty response
is returned
• RedirectResult - Performs an HTTP
redirection to a specifed URL
• RedirectToRouteResult - Performs
an HTTP redirection to a URL that is
determined by the routing engine,
based on given route data
• JsonResult - Serializes a given
ViewData object to JSON format
• JavaScriptResult - Returns a piece
of JavaScript code that can be
executed on the client
• ContentResult - Writes content to
the response stream without
requiring a view
• FileContentResult - Returns a file
to the client
• FileStreamResult - Returns a file to
the client, which is provided by a
Stream
What are the subtypes of ViewResult class?
As it is a concrete class, so subtypes are not
available for ViewResult class.

2. • FilePathResult - Returns a file to
the client
3 Example:
(OR)
"ActionResult" can be used to exploit
polymorphism and dynamism. So if we are
returning different types of view
dynamically "ActionResult" is the best
thing. For example in the above code
snippet we can see we have a simple action
called as "DynamicView". Depending on
the flag ("IsHtmlView") it will either return
"ViewResult" or "JsonResult".
Example:
4 When to go for ActionResult class ?
If our action method may have different
behavior, like either render a view or
perform a redirection. We can use the more
general base class ActionResult as the return
type.
When to go for ViewResult class ?
If we are sure that our action method will
return some view page, we can use
ViewResult.
Reference:
http://onlydifferencefaqs.blogspot.in/2014/03/difference-between-actionresult-and.html