I actually downgraded back to v5 because of the terrible changes they made to Web Inspector in v6, so I'm pretty annoyed that they didn't even mention it when introducing the new version -- at a developers' conference, no less!
The tools save all the robust features added in 6.0, but they sent a designer to go over them again in 7.0 so it's pretty and powerful now.
Here's a screenshot of me running the Safari 7.0 dev tools in the multi-monitor space:
When I have a lot of work to do debugging something, I switch over to Chrome which still has the old style layout, because I find it much easier to use.
The interface in XCode isn't bad. My big problem is that you can't view source any more, it's crammed in that panel. The list of requests? Crammed in that panel. JS console? Inspecting elements? All crammed in there.
I always feel light I'm fighting to find what I want instead of switching between things I might need.