Use an indent of 4 spaces, with no tabs. This helps to avoid problems with diffs, patches, CVS history and annotations.
For Emacs you should set indent-tabs-mode to nil. Here is an example mode hook that will set up Emacs (ensure that it is called when you are editing PHP files):
(defun php-mode-hook () (setq tab-width 4 c-basic-offset 4 c-hanging-comment-ender-p nil indent-tabs-mode (not (and (string-match "/\\(PEAR\\|pear\\)/" (buffer-file-name)) (string-match "\.php$" (buffer-file-name))))))
Here are Vim rules for the same thing:
set expandtab set shiftwidth=4 set softtabstop=4 set tabstop=4
It is recommended to keep lines at approximately 75-85 characters long for better code readability. Paul M. Jones has some thoughts about that limit.