I think you can use it both but what I think that E/Z nomenclature is used when your substituents are some groups other than hydrogen atoms, and if you have hydrogen atoms in both sides you use cis/trans. http://www.chemguide.co.uk/basicorg/isomerism/ez.html

E/Z can be used always, it is general. Cis/trans can be used only in specific cases.

E/Z is general and can be used always. Cis/trans is correctly used only with disubstituted double bonds. In tri- and tetrasubstituted double bonds cis/trans is not defined; E/Z is then the only way for specification. Cis/trans is also used to specify the position of substituents in a ring.

When there are three or four different groups attached to the carbon atoms of a double bond, a pair of geometric isomers exists, but it is sometimes difficult to assign cis or trans designations to the isomers. we can say that they are trans or cis to each other. However, we cannot name the structure in its entirety as being either the cis or trans isomer. Because of the ambiguity in cases of many types, a more general system of isomer assignment, called the (E) and (Z) system, has been devised. The E and Z system is based on an assignment of priorities (not to be confused with nomenclature priorities) to the atoms or groups attached to each carbon of the double bond.