Obviously, there isn't good polling data for support for the revolution, but the information I can find puts estimates at 40-45%, with support for the Crown at between 15-20%. I wouldn't put too much weight on even that, though.

The popular 1/3 each for, against, and indifferent to the Revolution seems to be based on misinterpreting an 1815 letter from John Adams to James Lloyd recounting his estimate of support in America for France and the French Revolution in the US ca. 1797 (with the strong anti- side being supporters of England and opponents of the Revolution, and the neutrals being indifferent between England and France that would attach to one or the other side based on transient circumstances.)