I use SQL Admin Studio as it has a customizable template engine (I used it to write Delphi code to access stored procedures). It adds the following code to the top of the generated scripts so you don't have to worry about whether the stored procedure exists or not. Note that it creates the script in an editor so you can work with it before executing it.

IF EXISTS (SELECT * FROM sysobjects WHERE id = object_id(N'[dbo].[MyStoredProcedure]') AND OBJECTPROPERTY(id, N'IsProcedure') = 1)

DROP PROCEDURE [dbo].[MyStoredProcedure]

GO