DROP LOGIN [TestLogin] is the current method
sp_droplogin is the old method and will be removed from SQL at some point.
From your other post:
" ... when iam deleting the login ,automatically user also deleted in GUI....
So I want t-sql script for automatically delete the user when i delete the login belongs to that user....."
Use the GUI, then choose "Script Action" to generate the t-sql script. "Script Action" is useful to see the t-sql for many of the GUI functions.