Hard to pick just one. All The Lovers, Shampain, The Edge Of Glory, We Found Love, Diamonds, Call Your Girlfriend, Instant Crush, Keep You On My Side and Into You all come to mind.
Omg Instant Crush
That, Midnight City and Dancing On My Own are also the best
hello
your type
love me like you do
teenage dream
wide awake
the edge of glory
masterpiece
wrecking ball
we found love
dancing on my own
chandelier
wildest dreams
But the greatest of them all is All You Had to Do Was Stay.