lol.... well, you're the first person to call ef "erotic" That's unique for sure; can you elaborate with erotic, or link some images.
I've only seen like 3 episodes of memories. It was pretty fun with the eyepatch girl, Miya Miya is adorable, and the fact that Yuuko seems to have the ability to suddenly appear and disappear like... Batman!
ef: A Tale of Memories has two plots running side-by-side, with one romance in each one. Both plots are pretty good, and make for good romance drama and suspense. They utilize very nice plot devices and SHAFT's visual style to maximum effectiveness. I highly recommend it.
ef: A Tale of Melodies I've only watched a little bit of so far. This anime is pretty erotic in many scenes, I have to say, lol. It's not quite as good as Memories, but its pretty good so far, and it has that Denpa Onna fun quality to it, if you know what I mean.
Oh, and great review of Usagi Drop. You said so much there that I wasn't sure how to respond, lol.