I would have to suggest that more or less waterproof is moot in either fabric, it's mainly the DWR coating that sheds moisture and both will give up under any concentration of water. I think Pertex primarily addresses breathability, windproofness, and, subsequently, durability. In my experience microlight is less breathable but more durable and windproof; quantum is the reverse, but neither to a fault. I really want to stress that. Both are great, modern fabric technologies with subtle but notable differences that are mostly personal preferences derived only from experience.
Unfortunately, this doesn't help the initiate: as I can personally recall from my own debate with the dharma of windshirts. You'll still struggle between the forces of breathability and windproofness. But, as I eventually experience with any gear concepts, just go for it. Get a deal, or grab what's in front of you, and find out for yerself. You really won't go wrong with any of the high quality gear we've recommended, you can only learn more.