My first inclination is to buy the 85L. It is really special, but, does have issues. One problem with it is that you must take extra care (i.e., time) when attaching it/removing it to protect the rear element and to make sure to retract the extending front element before removal. There's also the question of critical focus and the limitations of the 5D2 only having a cross-type AF point at only the center position; that can limit how well you could shoot the 85L quickly wide open.
However, as you know, lens are very heavy and can take up a lot of room. I personally would always want to have an acceptable single lens standard zoom option. So I would either get the 24-105 or 24-70 to fill that role. For me, it would be a higher priority than the 85L.
If you can accept the limitations of shooting primes over the convenience of a zoom, I'd recommend the 85L. That upper body portraits with it or head shoots makes it worth while to me. I definitely see the 24-70 the safer solution for most people who aren't sure. If you are seriously in doubt, I'd rent a 24-70 and maybe a 85L to learn what you can live with.