Upvote:2
98% of Christians are Trinitarian. Unitarians make up a huge majority of those that are not. However "Unitarian" is also the name of a number of denominations, and so tended to be avoided unless applied to those denominations. This makes it not very helpful to refer to those that are not Unitarian.
The number of Binitarians is extremely small (tens of thousands) and many people will divide Christians into Trinitarians and Unitarians, neglecting the outlying exceptions.
If you had to make such a reference then "non-Unitarian" would be fine, as long as you make it clear whether you mean those not in the denominations or a more general meaning.