Many years ago Dean Torges did a test at which finish was the most effective at keeping out moisture. The top two were, melted paraffin wax, and shellac. They scored much better than varnishes, oils, or oil/varnish mixes like tru oil.
If moisture protection is your priority then these are your best choices.
You may also want to consider the cosmetic effect of a finish on white woods. If you want to maintain the natural appearance of a white woods, then paraffin, and white shellac will do the best job. Garnet shellac on whitewood doesn't look very nice. Oils etc yellow the white wood.
If your bow is for hunting then most people like to stain whitewood, you can use an oil based stain to darken/camoflage the brightness of the timber. Water based stains, or alcohol based stains, will likely run if you try to put paraffin or shellac over these finishes.
Tru oil is a good finish. It looks great, and is relatively easy to apply,and relatively easy to touch up. Its only average for moisture resistance. None of the finishes are ineffective, they work fine. They're just not as effective at keeping out moisture as paraffin or shellac.