I've recently finished reading both of these manga series. Usagi Drop is 9 volumes long, and Mirai Nikki (or Future Diary) is 12 volumes long.
Putting thoughts under cuts because of spoilers.
Mirai Nikki
Volume 12 has been out for a while, but I only just recently got to getting my hands on a copy and reading it. Up until volume 11, I could take it... but some of the content in 12 just felt... rushed? thrown in? plot-goes out the window? It's hard for me to accept that the reason why Yuuki (parallel world #2) likes Yuno (1) is because like his parents, he grew to love her because she was always with him. That analogy just sounded wrong to me. Not to mention, she's killed a lot of people (though he had killed a couple of his friends, too....). Beyond that, the other thing I couldn't wrap my head around was that Yuuki (3) gets paired with this other lady (I don't remember her from before, but she must have been from before), and Yuno (3) gets Yuno's (1)'s memories from Muru Muru (1) and goes back for Yuuki (2). And 9th (2) with that cop guy (3)... too much craziness.
It's awesome that this series is getting an anime, but I wonder how they're going to end it...?
Usagi Drop
I'm so disappointed with the ending of the manga... =( I loved loved loved the first arc where Rin is 6 years old. The arc ended right where the anime decided to end. But then I continued reading, and they do a 10-year time jump to where Rin is 16 years old. There are flashbacks to some of the years inbetween, but to see that Kouki did (or didn't really do) things that shot his chances with Rin, and that Daikichi and Kouki's mom never get together... that's just really sad. And I saw where the hints started dropping about Rin's feelings... and I was like, "Please, no.... get with Kouki! He cares for you so much!" Why, Rin??? Why did you have to change your relationship dynamic with Daikichi??? I also realized that once the 10-year jump occurred, no longer was there the text that said that this was a heartwarming story of Rin and Daikichi. Why ruin that??? OTL
If you want this series to remain that pure, heartwarming feeling... do not read the second arc of the manga.