One who is performing a Pidyon Ha’ben for his firstborn son should preferably find a Torah scholar who is a Kohen, and give him the Pidyon Ha’ben money. If he can find a Kohen who is a Torah scholar and also poor, then by giving him the Pidyon Ha’ben money he fulfills two Misvot – Pidyon Ha’ben, and charity.
However, although there is value in selecting a Kohen who is a Torah scholar, a family member who is Kohen takes precedence over a Torah scholar, in accordance with the principle of "U’mi’besarcha Lo Tit’alam" – one should not "ignore" family members. Certainly, if one has a relative who is a Kohen and also needy, then this relative certainly takes precedence over a Torah scholar.
One should not select for Pidyon Ha’ben a Kohen who flagrantly violates Shabbat. It is possible that the Misva is not fulfilled if the money is paid to such a Kohen, as he might not be considered a full-fledged Kohen.
The Misva is fulfilled by giving the money only to a Kohen who is above the age of Bar-Misva. However, the Kohen does not have to be married for the Misva to be fulfilled.
Anybody who is generally presumed to be a Kohen, and is treated as a Kohen with regard to other Halachot (such as receiving the first Aliya in the synagogue), is eligible to receive the Pidyon Ha’ben payment. Of course, if it is discovered after the Pidyon Ha’ben that the one who received the money is not actually a Kohen, one must perform a new Pidyon Ha’ben and give the money to a Kohen.
Summary: It is preferable to choose a Torah scholar as the Kohen for a Pidyon Ha’ben, though a family member who is a Kohen takes precedence over a Torah. A flagrant Shabbat violator should not be selected as the Kohen for Pidyon Ha’ben. The Kohen must be above Bar-Misva age, but does not have to be married.
