My father has used both Penzoil and Evinrude oil in his Evinrude outboard motor. A lot of this has been because of the oil that was available to him at the time. If he could find one but not the other at the marina store, then he would buy it. Both of them were not usually available in the same store at the same time, so he never really had to decide.
From using both types of motor oil, he has started to recognize differences between the two. He has seen that the Evinrude XD 50 oil produces a lot less smoke. This is important for him, because he, like most boaters, cares about the environment.