tmux - more modern, less crufty.

If that's too short an answer, look at configuration examples for screen vs. tmux: screen's configuration is so arcane it's impossible to read.  The absolute worst is attempting to configure the status bar (assuming you use that).  tmux's config isn't great, but a normal human being has some hope of actually reading it.

You should also look at Byobu ( http://byobu.co/ ) - I prefer my terminal multiplexer raw, but you may not.