Dean:
The Impala. You love just to cruise around togheter, no destination, just driving. Dean says he's happiest when he hangs out with his two Babies at once.
Sam:
A coffee shop. Any coffe shop available. You get to be alone, away from Dean and Cas, just the two of you chatting together. It's the little things that matters the most to you.
Castiel:
Your favorite place together is the sofa, a place where you can cuddle and watch television, just relaxing. You with Cas' arms wrapped around you one of your hands locked with his. It's the best part of the day.