Eddie I agree with you on most every post but advocating flex over hard pan duct because someone can't seal them correctly is something I can't get on board with. So much pressure drop and potential for kinks/restrictions with flex.To be clear, I should have said it was very hard to find an HVC contractor that would create the metal duct to go from the closet to the attic. In the end, I found several and went with the bid from the contractor that did the big commercial jobs in my area, including the airport. I believe that they did a good job making it, and that they did a good job of sealing it. But I was in a house last week out at the lake that is considered very high dollar, and it has both metal and flex ducts in it's attic. Guess which ones where keeping me cool while I was up there?
To say that metal is better because it flows better ignores the simple fact that metal ducts leak and flex ducts don't. While you might have your ducts sealed good enough to never leak anytime in the future, odds are very good that if you look at ten other systems with metal ducting, 9 of them will have leaks. In my opinion, best practice is to use what will offer the best chances of success over the longest period of time.
Here's a few pics coming off one of our two hvac systems in the home. Red and green lights are the zoning dampers. All custom hard pan and even the short runs off trunks are hard round metal including those in our basement into our drop ceiling. Not a single piece of flex and proper sealing at all seams.