Well, "The Angels take Manhattan" has got no chance, I'm even surprised it's been nominated. It was way too flawed.
"Asylum of the Daleks" had the potential to be one of the best DW episodes ever, but threw it away by trying to do too much in too little time all the while having the running-around-to-appear-fast-paced that Moffat always does (yeah, I know they did that a lot on Classic Who, but they didn't have the budget to do other action, while Moffat does have the budget, and uses it, but still adds lots of running-around).
"The Snowmen" was Moffat's best christmas special, yet, it might have had a chance.
But, ultimately, "Blackwater" was way too big and good an episode for anything else to have a chance against it. Maybe they should hire him to write for DW.
*cue outcries of: "Oh, no, that would make him finish Ice & Fire even later!"*