It is quite difficult because players like Lennon are imperative to the balance and work rate of the team whilst being capable of moments of brilliance. Then again, Bale has been quite astonishing at times and has been responsible for so many decisive moments. Then you look at Lloris or Vertonghen and think without either then our system doesn't work, the system we employed to such good effect for three months. Finally, you have Sandro or Dembele both of whom work so well together - so much so, Sandro doesn't get injured I feel certain we would be 6 points better off (that isn't a scientific approach I just think we would have won against Fulham and Liverpool with him there).
I am going for a more emotional decision and going for Dawson. Turned down QPR, loves the club and fans (reciprocated) and, despite some weaknesses still plays very well and never, ever looks like giving less than 100%.