Interesting question. I think they're all low eras over all but certainly not the LOWEST runs of books ever (yes, I'm referring to HWSNBN in UXM.)
I'll be honest though for ANAD I only read Bunn's UXM , which I thought was fantastic and maybe the best book we've had since Mike Carey's run. I was going to drop Marvel completely after Secret Wars but who was I kidding about not reading a title of UXM, I'll read it even when it's bad. Also read the first arc of Extraordinary X-Men thanks to Kindle Unlimited. BLAH. Based on reviews and summaries nothing else piqued my interest and I got the feeling it was completely not worth reading. so while what I read, I 100% liked, it was only one book. Oh! and I did read the events: death of X and IvX...good god. DoX was decent as a stand alone but the whole concept of what Cyclops did was poorly poorly executed. IvX was a disaster.
I pretty much read all the books during Marvel Now! and while there was nothing really all that interesting, and at times boring, none of it was flat out awful. I don't like Bendis' writing, and never really have, and he did helm that era, but he has good ideas that he for the most part can't execute very well, and absolutely has a problems with endings. So while I was very interested in the first year the story just went flat...still...the none core books were good particularly Remender.
I"ve been reading most of the books during ResurrXion, and what a mixed bag it is. It started out looking pretty awesome, but the (to me) flagship book, Gold, is really bad. Blue is not awful but it's not that interesting either, mainly because the 05 and alternate universe characters (for the most part) are wearing thin on me. But the Mothervine storyline is good. Astonishing's first arc was great but the second one is falling flat. Weapon X keeps getting worse and worse and was never that great to start with. LOVED Phoenix Resurrection and am loving Red so far.
So for all that, I'd have to say my least favorite easily was ANAD despite having my favorite book of all three eras. Everything else sounded awful. One good cookie in a batch doesn't save the batch. and it's close with the other two but i think I have to give Marvel Now! the slight upper hand. While its few highs have not reached quite as high as the few highs from ResurrXion, its lows aren't going as low either. Sometimes being bland isn't such a bad thing.