"X vs. Y notation(s)" - Pluralizing the noun in "adjective-noun" comparisons

I have a document about programming, one of the sections of which describes the difference between an array notation and an object notation.

I don’t understand whether I should pluralize the word notation; that is, whether to choose

Array vs. object notation

…

or

Array vs. object notations

…

Or maybe both versions look very unnatural and should be replaced with

Array notation vs. object notation

…