Hi Rod,
Both timbers should by their nature give a good finish with two-fluted cutters.
Do a trial run first as sometimes you can get endgrain tearout on some timbers that is hard to predict. If on trial you do experience tearout, I have found it helpful to rough out the cut. A very light finishing (25thou) cut does not usually give tearout then. Keep the cutter sharp!
Another thing a test run can do is to give you an indication of which direction of cut gives best finish. This is not always what you might think by looking at the grain.
Something else that can be a huge help is to run a vacume cleaner nozzle beside your cutter especially if routering small narrow or deep cuts, for example for inlay banding. It keeps the track clear of re-circulating sawdust and helps you to see and gauge forward speed better.
If upward tearing is a problem you can sometimes start by setting up a fence or guide for the actual position of the cut . Then clamp a thin piece of timber on top of the timber you intend to router. The fence, already set to position, will still guide your cut and you should get a clean top edge to the cut.
John