The interior of the 6 is a nicer place to be, with higher perceived quality of the plastics, but the 5 is actually better screwed together inside in my view - more screws & clips etc
Paint is vastly better on my 5 than 6.
The 6 is peppered with tiny chips and the soft paint scuffs at the merest hint of anything touching it...the 5 is twice as old, has never been polished and has a far better coat of paint, that chips less, is less orange-peely and more resistant to scuffs.
Oh, and the 5 has a better coat of paint on the areas you don't initially see.