Keirsey, David. September 17, 2007. <http://www.keirsey.com/pumII/dimensions.html>.
Keirsey, David (1998). Please Understand Me II. Retrieved September 17, 2007 from http://www.keirsey.com/pumII/dimensions.html.
I personally prefer the APA Style because it gives the reader more information regarding the source. As for the quotation within your paper, it should look like this:
“[…] Jung and Myers were trying to figure out what the different types have in mind, while I am trying to figure out what they can do well under varying circumstances”1.
Regarding the reference, you can either use an endnote (at the end of your paper) or a footnote (at the bottom of the page on which the quote is cited). Again, if you choose footnotes, you must stick with it for all of the other references in a same paper. I personally prefer footnotes because the reader can look at the source’s reference very quickly (it’s on the same page).
Here’s an example of how your footnote / endnote should look like if you decide to use the APA Style:
1 Keirsey, David (1998). Please Understand Me II. Retrieved September 17, 2007 from http://www.keirsey.com/pumII/dimensions.html.