This answer would be related to design - and personal bias.
For me, left justified is the easiest to read (for those languages
that read left-to-right). Thus, if I have a lot of text on the page I
will left-justify it.
Centered can be used for headings and other such brief interruptions
in the flow of the text.
Right-justified is very difficult to read and should only used for
very sections of specialized text, like poetry or headings.
Full-justified would be nice, but tends to add extra spaces between
words (in order to justify the right margin). That's why you sometimes
see odd lines with dozens of spaces between just two or three words on
the line. Because of this odd spacing the line becomes difficult to
read.
If you want people to read your page (there is lots of text), then you
should stick to left-justified (again, for a left-to-right language).
If you are attempting to achieve some sort of artistic look to your
page and there is not much reading (like a page of photos or
something), then use whatever looks best. For short sections of
"specialized" text (like a menu), use whatever you think looks good.
--George