If you can make the extra effort, a thread chaser is preferred over a tap. From the bottom right of this page on thread repairs:



"This is a graphic example of why you should use a thread chaser instead of a tap or die to clean threads. These two ARP head bolts actually have rolled threads. Running a normal die over the bolt on the right removed a lot of metal, weakening the strength of the bolt."

But really if you get the work done at a quality powder coating shop, you shouldn't have to chase any threads.