Basically, tmux is a lot more flexible and easier to hack than screen. I've never bothered with tmux though, screen is good enough for me.
I think HD quality is overrated. Yes, I can tell the difference. Yes, I appreciate HD quality. But up until 2003 or so, I happily watched live sports in standard definition quality without feeling in the least bit cheated. So I see no reason why high quality is mandatory today.