Dear Student,

Basically, the stability of Alkyl Free Radicles follows the order given below.

Methyl < Primary < Secondary < Tertiary.

This means that the Tertiary Free radicles are most stable from these. Now, as you have not provide us the figures of species, so it is difficult for us to tell the most stable radicle.  You can post a new question with proper diagrams. Only then we can help you. But, you can yourself check the most stable radicle by using the series mentioned above.

Hope you understand.