Retrieve Current Date Time in SQL Server

There are three ways to retrieve the current datetime in SQL SERVER.
CURRENT_TIMESTAMP, GETDATE(), {fn NOW()}

CURRENT_TIMESTAMP
CURRENT_TIMESTAMP is a nondeterministic function. Views and expressions that reference this column cannot be indexed. CURRENT_TIMESTAMP can be used to print the current date and time every time that the report is produced.

GETDATE()
GETDATE is a nondeterministic function. Views and expressions that reference this column cannot be indexed. GETDATE can be used to print the current date and time every time that the report is produced.

{fn Now()}
The {fn Now()} is an ODBC canonical function which can be used in T-SQL since the OLE DB provider for SQL Server supports them. {fn Now()} can be used to print the current date and time every time that the report is produced.

If you run following script in Query Analyzer. I will give you same results. If you see execution plan there is no performance difference. It is same for all the three select statement.
SELECT CURRENT_TIMESTAMP
GO
SELECT {fn NOW()}
GO
SELECT GETDATE()
GO