That’s a tough question… selecting a single favourite is never possible for me. 
I like each photograph I take for different reasons, sometimes because it’s
technically excellent, some because of the subject, sometimes for fun. 
I have an awful lot of favourite photographs.  This is one of them, and
it’s a favourite because is a serendipitous great shot.  Only rarely do I
catch an unexpected gem, but that’s what this is.  Taken on the fly,
out the car window.  With the saturation pumped for a bit of glam. 

The same applies to other people’s photographs.  Again, I’ve a lot of favourites.  
This one because it’s fun :)