Annuity Trust: The income is predictable and fixed. When you establish the trust, you set a reasonable and permissible fixed annual income (based on a percentage of the initial market value of the assets). Even as the value of the trust fluctuates, your income remains the same - except in the very unlikely and uncommon event the trust is exhausted.
Unitrust: The income varies on an annual basis. At the establishment of the trust, a reasonable and permissible income percentage rate is determined. Annually, the trust assets are valued, and the established rate applied to the annual value determines your income. As the trusts assets increase or decrease, your income increases or decreases.