1. Polyester urethanes are more durable than acrylic urethanes.
It may be helpful to define our terms here. When Cruzin9 refers to durability in this context, I'm sure he means impact resistance, flexibility, and toughness. I would agree that polyester urethanes generally have better impact resistance, flexibility, and toughness than acrylic urethanes.
The reason for my post is, when reading coatings literature, you'll often come across references to exterior durability referring to gloss and color retention on exterior exposure. So as not to cause any confusion, acrylic urethanes as a class will frequently exhibit better gloss and color retention than polyester urethanes. So, don't be surprised if you read statements to the effect that acrylic urethanes typically have better gloss and color retention, which may in some contexts also be referred to as exterior durability.
It's not that either statement is wrong, they are both right if the term durability is understood to be used in the correct context. I hope this might help clarify any possible confusion for interested readers.