If we were to apply each of the different approaches consistently, then we get:
Lowest scoring dance: Caroline's Cha-Cha-Cha, Frankie's Waltz or Charleston, Mark's Cha-Cha-Cha, Simon's Rumba
Mistakes to correct: Caroline's American Smooth, Frankie's Samba, no clue for Mark, Simon's... Paso maybe?
Journey: Caroline's Cha-Cha-Cha, Frankie's Cha-Cha-Cha or Foxtrot maybe?, Mark's Cha-Cha-Cha, Simon's Jive probably
Breakthrough: Anything Caroline did between weeks 2 and 5 probably or her Jive, Frankie's Paso or Tango, Mark's Samba or Jive (maybe QS at a push), Simon's Charleston
In 2011 they chose two dances that had scored 39 to begin with and had been done just two or three weeks earlier plus one which had scored 36 in week 3, in 2012 it would seem to be the 'breakthrough' approach and in 2013 it was three dances that were good the first time but could be improved (two of which hailed from week one and the other from week 10) plus one that had been completely botched the first time around.
And in 2010 it was the couples' highest scoring dance by default, which to be honest strikes me as probably the best way if they're really going to pretend there's any kind of logic to this and would have left us with Caroline's salsa, Frankie's VW or AT, Mark's Charleston and Simon's AT, Waltz or Foxtrot.