its a tough question...but generally the more effortless shots that produce power, feels the best.
I have been struggling with my topspin DB for a while and recently changed technique. So it feels great getting any sort of power and fluidity on that shot.
There is also this shot when your are forced to do a running backhand (or forward on the run), and you hit a clean slow controlled winner with slice down the line...especially when using disguise or around the net post - totally fooling the net player in doubles. More of a finesse shot.