Great comments, completely agree it's all about connection - with my partner, the music and possibly an audience if there is one!
As a lead, there's so much on you to make the dance happen that the really memorable dances are when everything I want to do just seems to click and I manage to hit everything in the music - combined with that great connection you talk about above.
Haha generally don't tend to hit these heights unless I've been dancing solid for at least a few hours!
It's all about energy for me, it kind of builds throughout a night and each dance.
Also, think a big part of connection is when my partner is really relaxed, trusts me, is enjoying themselves and above playful.
Nothing saps my energy like a face like a slapped arse, or a dance that feels like a fight :)
I suppose in summary, it's when all the stars align: music, partnership, moves, energy, playfulness - when you both step away going wow that was pretty special and can't wait to dance again!