Which compound in the above pair undergoes a faster SN1 reaction?

In the SN1 reaction, the big barrier is carbocation stability. Since the first step of the SN1 reaction is the loss of a leaving group to give a carbocation, the rate of the reaction will be proportional to the stability of the carbocation. Carbocation stability increases with increasing substitution of the carbon (tertiary > secondary > primary) as well as with resonance.