I don't find AppCode's navigation superior to Xcode's for Objective-C and--at least the last time I tried the C++ extensions to AppCode--completion wasn't any better for C++ than Xcode's (which I figure is probably a clang limitation).
I very much like IDEA for Java or Scala, but I find myself frustrated when I use AppCode.
AppCode has such nice navigation and completion.
It all makes me wonder how on earth anyone could say they enjoy xcode.