I do believe that Tim Cook remains the best person to lead Apple.
When you look at the current business climate, there is literally nothing that companies like Microsoft or Samsung can do to threaten me as an Apple user. Rather, the biggest threats facing Apple today are forces like the FBI, Donald Trump and foreign governments. These pose significant risks that could derail Apple's business model overnight.
In this regard, Tim Cook is the steady hand that Apple needs to navigate these political challenges (can you believe that some haters would rather Apple be run by a loose cannon like Elon Musk?). I foresee him continuing to lead Apple for a good many years to come, and I can't think of anyone better suited for this role at this current time, given the challenges Apple faces.