I'm sure the latter points can be remedied by config file settings for screen, but it's nice to use software that just works once in a while.
I'm glad that there is competition in this space, but you tmux evangelists need to realize that there is a lot of work that needs to be done before tmux is really "an amazing improvement to screen."
Is vertical split in mainline screen now, or do you still have to patch it?
I use both tmux and screen but prefer tmux. Here are some (non-ideological) reasons:
Dunno if screen has this, but in tmux IIRC, you can have two different tmux servers running in totally different processes, and transfer a window from one server to another. That's pretty cool, imho. The graphical equivalent would be running two VNC servers, and moving an xterm window from one to the other.
Another cool thing: pipe the entire contents of a window in realtime to an arbitrary program.