PostScript files, being printable and viewable on screen, are the most useful. However since some of them must be processed by hand at SLAC, they are usually delayed a day or so beyond the TeX files and are not available for all bulletin boards. TeX files are the form submitted directly by the authors. They often use certain standard macro packages which you have to have on your system to process them. Many journals now handle submissions by e-mail, as well as other correspondence, refereeing, etc.
Details vary by journal, so check a recent issue before sending.
For a few pointers, see the resource catalog Be sure to ask about figures. Others may request a fax submission to be sent to referees with originals to follow by regular mail. This is a subject of active discussion. You might want to read or participate in the APS E-Print Archive Forum . Nuclear Physics requires that you be a subscriber to browse even their meager experimental on-line data.