To determine which tefillin are right for you, we must answer the following four questions:
Concerning the ksav, which minhag does your father follow - Ashkenaz, Sefard or Sefaradi?
(Note: Ashkenaz = Beis Yosef and Sefard = Ar"i z"l)
Are you right handed or left handed? Your tefillin will be put on the opposite arm answered to this question.
Does the knot on the back of your father's shel rosh look like a "daled" or a "square"?
Does your father wrap the retzuos of his shel yad "in" or "out" ? (Note: "in" is most common for ashkenazim whereas "out" is most common for chassidim and sefardim)