Depends on what you do.
I use a 24-70 f/2.8L and it's a good carry around lens. Others use the 28-300L and I looked at one and considered it too heavy for a walk around lens but others swear by it. It would be good if you want one lens when travelling.
I don't think there's such a thing as a universal lens, the 28-300 comes close (haha) but some people say it's too soft at one end or another and there are a lot of trade-offs.
On my 24-70, I find myself zooming to 50mm anyway, so sometimes I just take my 50mm if I don't have any real plans.
I read about some famous photographer who taught students to start with the 50mm and run back and forth.
The 24-105 is a pretty good compromise.
So, whatever floats your boat.
Daryl