`#defined` constants (at least from what I have read) are, for all intents and purposes.. interchangeable with the  long form, double declared `extern NSString *const` syntax.

The  difference that I can't help but focus on is...  8 words, over 2 files... vs 3 words.. in 1 file.  

You've probably noticed.  I am a brevity freak.. I could go on and on about why.. but as long as it doesn't sacrifice the expressiveness or function of the code.. I am all in favor of reducing any distraction that can be avoided.