I want Haibara/Shiho to end up with...

[Suutashi]

Mitsuhiko if she remains a child, Hakuba would be interesting if she reverts back to adulthood.

[phreak_91]

Mitsuhiko if she remains a child, Hakuba would be interesting if she reverts back to adulthood.

Mitsuhiko either way

[Vylash]

I personally want her to remain alone in a romantic sense, but continue being friends with the DBs, I don't see why she needs any sort of love interest

[Female Apprentice]

I'd love her to get together with Mitsuhiko. 

She has to stay I child of that, of course. I know this would disappoint many Ai/Shiho fans.But, although she would be bored to visit school again as a genius, I think it's very likely that she stays a child and somehow catches up her childhood. Also, it wouldn't really make sense to become an adult again, since, after the BO is caught and destroyed, it's likely that FBI wants her to join the witness protection programme.
I don't know if she'll ever overcome her panicky fear of any BO-member, but even if she did, it would be not very good for her safety to just get back into Miyano Shiho while there are still people who want to kill her (even when in prison). So why don't we skip all the stress and stay Haibara Ai?
Mitsuhiko would be the best man for her then, since he would be in her age (somehow ...).
And we all know that he's a smart kid and that he'll be a good detective some day. 
Maybe not as good as Shinichi, but Ai (hopefully) could get used to this. 

[Natasya]

Mitsuhiko for me~
But, Saguru Hakuba is also fine either way

[ranger]

mitsuhiko can die

[miikosan]

I'd prefer her to stay single. What makes her so likeable is her sarcastic and teasing personality. If she starts going out with someone, I don't think she would stay this way.

If I must, however, I'd pick Okiya.

Spoiler:

And hope that Okiya isn't Akai.

[IHKF]

mitsuhiko can die

D:

WTH ranger? XD LOL

[phreak_91]

mitsuhiko can die

D:

WTH ranger? XD LOL

Look on the bright side.  At least he didn't say Ayumi.

[tanteikun1412]

Mitsuhiko

If she didn't want to be back normal.

If she want, then I don't know.

[pofa]

She's been terrified of Okiya for forever, so I can't see her jumping into his arms somehow. (Plus he's kind of a douchebag--sorry Kleene D: )

Araide she's never actually met afaik. :V

Akai, same as Okiya + dated her dead sister.

Mitsuhiko is 7.

Hakuba, see Araide.

A character that's not appeared yet would have to be really impressive not to feel forced. :V Then again, a lot of the relationships in DC are pretty forced, so I guess Haibara wouldn't be an exception.

[ProfParanoia]

Mitsuhiko is 7.

It's okay as long as the pre-pubescent child being taken advantage of is a boy. That's just something boys do, and I think he called dibs.

[pofa]

It's okay as long as the pre-pubescent child being taken advantage of is a boy.

:x Not going to lie, MitAi creeps me out for just that reason. I know Gosho is all fluffy about him having a crush on her, but I would have a serious problem if it were a two-way street.

Edited because, thinking about it, still no.

[AICHAN]

I still think Okiya is the better choice for her,even if he's Akai.

[IHKF]

Okay, about the prepubescent thing....

Haibara probably WOULDN'T be interested in him currently. If she stays as a child, that almost makes her a child, in my opinion. The longer you act like something, the more you BECOME it. I won't say she'll revert back to being a small child intelligence-wise, but she may get more childish and cuter and forget a couple of things here and there. Meaning, she'll get more comfortable around Mitsuhiko and possibly establish a close friendship to all of them. (And no, I don't mean that her current friendship with them is acting...) If she grows into her years as a teenager with him by her side... don't you think that she might start getting a little closer or liking him as a little more than a friend?

Mitsuhiko is already smarter and more mature than most kids his age (all of the DB are, really...) once he grows up something tells me he can become the sweetest, smartest, shyest boy in the world (or a very bad rebellious teen who's tired of hearing what a good boy he is who knows how to hack computers and can articulate very complex plans to rob a bank, but I think just about everybody knows the first one is more likely. LMAO XD) and Haibara needs somebody like that. Haibara doesn't need to be made deadlier by somebody like Akai or somebody that will keep her on her toes worrying like Hakuba (he runs off as much as any of the rest of them do). She needs an opposite who's still so similar to her that she can talk to him and not feel like he doesn't understand what she's saying. She needs somebody who will admire her and love her but still gain confidence and put his foot down when she does something he doesn't like. She needs somebody who will make her a better person and draw her away from her old life full of guns and crime.

On the other hand, Mitsuhiko needs somebody who'll make him more confident, who'll teach him to step up to the plate and be a man and inspire him or make him do things that make him uncomfortable and to make him think outside the box. They need each other.

Isn't that what's truly BEST for the both of them?