Can't pick just one but my fave five are:

Colin Jackson & Erin AS
Zoe Ball & Ian Tango
Alesha & Matt Cutler Waltz
Scott Maslen & Natalie Jive
Pixie & Trent Foxtrot

I really miss the Cutlers being involved with the show. That Billy Idol jive Nicole choreographed is still my favourite ever group dance, I really wish she'd had a proper contender one year so she could have shown what she could do, and Matthew made dancing look so effortless, I used to love watching him.