From what I have read, dacron will typically save 10 pounds, +/_, over filed canvas.
In no particular order, the main factors to be juggled are weight, smoothness, durability, and time to apply (many canvas fillers take a month or more to cure). What is "best" depends on the relative value you give to each of these factors, keeping in mind how you will use the canoe.
In my particular case, I have found that all canoes weigh more as I age (I'm in my 70's) so I weigh "weight" more than I once would, and since I have found the 20 foot test to be the appropriate test for judging appearance, I also weigh "smoothness" less than I once might have. Different strokes for different folks.
Greg