Soon you will be able to get both: http://code.google.com/p/iterm2/wiki/TmuxIntegration. This means that you will get iterm's native window splitting if you use tmux inside iterm or plain tmux if you are using another terminal
I welcome every effort to supplement the crummy OSX window manager, but the iTerm tiling system is sadly a false start.
They have the tab/split metaphor backwards. Real tiling WMs (such as ion3) put tabs on the individual split panes instead of having one global tab bar at the top - and for good reasons.
As it stands you can not, for example, drag an iTerm tile to its own window or group multiple sessions in one tile. This may seem minor to the casual user but is a showstopper for those of us who would benefit from the tiling the most.
