So unless there's an example I can't think of, we don't have
anything conclusive. I tend toward Duj 'ar wIghaj, because
the noun that 'ar is attached to is not allowed a plural
suffix, so why not avoid a plural prefix as well?
David makes an interesting case, though I don't know that I agree with it.
Rather, I think this is a great opportunity to subtly indicate the attitude of the speaker and take advantage of the rule that nouns don't need to be marked with a suffix to be seen as plural.
Imagine a scenario in which our speaker has been told to prepare for a hopeless battle. In one version, the speaker is depressed but realistic. In another version, the speaker is crazily optimistic. Something like this would go a long way to driving the pronoun choice (at least for me).