Your thyroid produces 2 hormones that have an impact on your bodies metabolism, T-3 and T-4.
T-4 is known as Thyroxine. This hormone is not that particularly active in the body for metabolism regulation. Its effect on metabolism are minute compared to the effects of T-3. T-4 is converted in your body to the more active form, T-3.
T-3 is known as Triidothyronine. This hormone has the greatest impact on metabolism. T-3 is non discriminative when it comes to fuel to burn, it will burn muscle just as well as fat.
Go with the T-3