Oh man, now it gets much much harder!
Unquiet Dead
It is less obvious, now, isn't it? Nothing against the three stories that have gone, but two are from the first production block which was wrought with trouble and the director never returned, one's the ultra-cheapo budget saver episode... the rest? Harder to sort!
Case in point - I'd have had Unquiet Dead in my top three. I think it's brilliant, it might even be my favourite Chris Eccleston story. But, garnering the lion's share of the votes. I'd have expected the Long Game out next. Didn't vote for it, but I'd have expected it.