Here's what I can tell you about Army Duck Cotton Canvas - used by all of the top tent manufacturers.
Army Duck is highly water repellent, but at the same time very breathable. Moisture that would typically build up a synthetic tent will pass freely through the fibers, resulting in a comfortable living environment at all times. When it rains, the fibers of 100% Cotton Army Duck will swell, making your tent more water repellent. There's a reason all the top manufacturers use this material.
There are a few different Poly-Cotton Blends out there, but the one I am most familiar with is a 65% Poly / 35% cotton blend. We use this mostly in our "Glamping" tents as it is easier to clean than canvas, will stay a bright white longer than traditional canvas, and is less likely to get mold or mildew in high moisture environments. Most of the tents we do for glampers the South use this material for for their setups - our hunters still prefer Cotton Canvas. As this material is mostly synthetic, it does not swell like Cotton Canvas will, which can result in leaks within your tent - especially along the seams where there are 1,000's of needle holes. If you are to go this direction, I would get a tarp to cover your roof to make sure you don't have any water issues.