Okay, second attempt without posting accidentally halfway through...
My choice would be none of these; it would be Night Terrors. It's absolutely awful and has no redeeming qualities in my opinion. It takes all the worst qualities of thay oft-mentioned clanger Fear Her and emphasises them (annoying child alien, drab council estate setting, generic concerned parent as main guest star, no discernible villain, ultra-low stakes). It manages to be boring and seriously irritating at the same time. Amy and Rory might as well be absent for all that they add and Matt is on autopilot. I would happily never watch it again.
As for the options above:
Aliens of London deserves to be forgiven for its sins. It was only the second story produced and is still finding its tone (fat farting aliens alongside Iraq War satire). It makes mistakes that the show learnt from and should be treated with due consideration for that. Plus, World War Three was my first episode, and I'm still here, so it must have been alright...
Love and Monsters is very poor. But it isn't totally without merit - Marc Warren and Shirley Henderson are very good and I actually really like the central ideas. Jackie's scenes are fantastic. But other than that it's pretty terrible, very tedious and unnecessary, and once Peter Kay starts chewing the scenery in that ridiculous green costume the whole thing descends into a nightmarish farce that I'm rather embarrassed for. But not the very worst.
Fear Her is not the very worst either, but again, it's pretty awful. I do think that most of its faults are worse in Night Terrors, but it certainly shows those faults. The whole idea is terrible and it's so astoundingly throwaway that I struggle to care about anything in the whole episode. The resolution is utterly stupid and the cartoon abusive father come to life is a serious "what were they thinking" concept. I don't mind the Olympic torch finale with Tennant but it does serve to highlight the awful deifying of the Doctor thay plagues the new series. It's a regrettable episode indeed.
I have no particular issues with Daleks in Manhattan. It's undoubtedly less than the sum of its parts - it had the potential to be an amazing story. And HumanDalek Sec is pretty rubbish. But I like the ambition, love the theatre climax, and it has some great moments. I don't see why this story gets such a beating.
Victory of the Daleks, again, is not that bad but it's certainly ly not awful. It's unrelentingly silly of course and the Mighty Morphin Power Daleks are rightly one of the most infamous misfires in the new series' history. Churchill is a complete caricature as well. But I kind of love the silliness, I like Matt's performance and as a massive Star Wars fan I just can't help but enjoy the spitfire laser battle. It's totally ridiculous though and I'm not a big fan.
The Curse of the Black Spot is terrible. It takes an immediately dull premise (at least five years' late with the "pirates" fad of the mid-00s) and makes it worse with lazy clichés, shameless stealing from other works and some really stupid lines ("a ship's a ship" in particular). Don't like this one at all and I don't really have any positives.
I love The Rings of Akhaten. I love the design, I love the look of it, I love the music, I (for once) love Clara, and although the story is extremely thin and it's all a bit wishy-washy, the goods totally outweigh the bads for me.
In the Forest of the Night is probably the runner-up in my "worst ever episode" list. Where to start? More annoying children, no real plot, not even a whiff of a villain (what is this modern trend with having no villain? I don't like it at all). Worst of all is Clara at her most unlikeable, deciding to condemn a bunch of 12-year-olds to fiery death without asking them if they would like to take the offer of being saved instead. Jeez. There's a scene which directly tells children to refuse medication without question. Wow. And that final scene - without a shadow of a doubt the worst final scene in Doctor Who history. Appalling episode.
Sleep No More is by a million miles the worst of Series 9 and a totally failed experiment. Found-footage doesn't work in Doctor Who, at all - and especially not when they choose to wuss out of it by not really sticking to the idea. It's unbelievably boring and the sleep-in-the-eye monster is just ridiculous. It gets points for ambition and for having a good performance from Reese Shearsmith, but that's it.
The Doctor, the Widow and the Wardrobe really isn't that bad. I love the magic of it and the music is one of Murray Gold's finest scores for Matt's era. Matt gives it his all and so does Claire Skinner. Yes, there are some terrible parts ("humany wumany" is a massive cringe moment) and not much particularly happens which is unforgivable for Doctor Who, but it's very well suited to its Christmas Day slot and I like what it was attempting to do. And the final scene is fantastic.
So a totally mixed bag of episodes. From the poll, I would choose ITFOTN but Night Terrors is definitely my personal worst.