So, on my device, when I set "desktop device" for a particular site, it continues to remember it. I don't have 4.4 on any machine yet because there's no reliable root for my devices, so I can't replicate your problem. Sorry.
ETA: However, there is an android add-on from Mozilla: Custom UserAgent String
Sorry, Safari for iOS does not allow you to change user agents. You'll either have to find relevant file in the backup, edit and then reload it. Or use a third party browser that lets you change user agents.
Another vote for Tapatalk
Same problem here. I have a old school phone and it is terrible to try to go on this site with it. Before the changes it looked just like the same site. Now it is really weird and messed up. You can't even go to the second page of any of the forums.
I vote for tapatalk