I will mark any helpfulposts with Kudos in future to make it easier to see from the main menu in case people think the issue is resolved.
I purchased ny RT N66u at the end of November 2012 and it arrived at the beginning of December. When I set it up there was a firmware update I believe and I duly updated it. There has been another update since then and am on .270 at the moment and it is stock firmware with no modifications.
I really cannot complain at the routers performance-quite the contrary really. It provides a very good signal and browsing or downloading via the router whether on wired connection or wireless is very fast and smooth. I get full signal on every device connected to it wirelessly throughout the house and I could never achieve that with the Superhub.
The only thing causing trouble is Youtube! I switched back to using the Superhub for a week as was suggested in this forum and it was ok to begin with but it deteriorated over a few days with really bad buffering on Youtube. So I switched back to the Asus and things have been a lot better in general.
Following advice in this thread I left my desktop on upstairs whilst watching a youtube video on my Nexus 10 last night. It started buffering so I went upstairs and watched the same video. This pc is connected via ethernet to the router. There was no buffering whatsoever. I went back downstairs and replayed the same clip. This time around it didn't buffer at all! Go figure!
I am starting to think part of the problem could be between the Youtube application on portable devices having issues with relaying the correct buffer stream and the several updates to the andiron Youtube app. They updated it on 22/2/13 and it keeps signing me out of my account on every device I have! It could also be down to a weakness in tablet or portable devices in general I think.
I will test out my theory with a desktop machine I have in the lounge which is connected wirelessly and see if the buffering continues on that device.