differences in between these env. variables

I've grouped these env variables, each group returns the same values is there a difference? which ones do you use? which ones should I not use for the purposes listed below group1 SCRIPT_FILENAME vs PATH_TRANSLATED where both return D:\Hosting\5291100\html\directory\file.php purpose: get the full file path to the php script group2 REMOTE_ADDR vs REMOTE_HOST where both return same IP purpose: get the visitor's ip group3 REQUEST_URI vs SCRIPT_NAME vs URL vs ORIG_PATH_INFO vs PHP_SELF which all return /directory/file.php purpose: get the virtual url to the php script