Provided you save the document in ASCII, using any text editor has no difference. For me I will prefer Notepad because it is a text editor, not a "word processor" that can save text files. But you can just use any other free/commercial text editors on Windows anyway. I will only use notepad when there is no alternative installed because it doesn't do syntax highlighting. For me, I install gvim on Windows. The choice is always yours.

Most likely you did not save the file as ASCII text, so it may become doc or rtf or something like that.

As a general rule, just make sure you are always saving the script as ASCII text, and always use FTP ASCII mode (if you use Binary mode, you have to use a Windows text editor that supports Unix EOL, and save the script with Unix EOL).