A while back I did some polls to see which of Usagi's and Mamoru's many, many, many suitors you thought they should have ended up with, so I thought it was long past time I did one for the series' other love magnet: Motoki.
My answer is a bit different for each of the three main continuities:
Live Action: Makoto. This is a no-brainer, really. Neither really has any other love interests in this series, and they were just an adorable pairing here.
'90s Anime: Minako. Mako's only really interested in him for like an episode, it's hard to take Usagi's crush on him seriously, Reika is a sleeping pill, and I can't remember he and Ami ever talking to each other? He and Minako interact at least once and seemed to have a bit of chemistry, and they'd certainly make a good-looking couple.
Manga: Ami. Again: Mako's only briefly interested in him (and I think she's better off with Asanuma or that cute horticultural club guy), Usagi's crush on him isn't serious, and while Reika at least has a personality, she still doesn't work as Motoki's girlfriend in my opinion. In the Sailor V manga, Motoki and Minako have a cute rapport, but I'm too much of a Reinako stan to really get behind them as a couple. Ami spends the Dark Kingdom arc crushing on Motoki (which makes "Ami's First Love" completely erroneous; should have called it "Ami's First Secret Admirer" instead) before that sub-sub-plot gets forgotten about completely, but he seemed to be impressed by her gaming skills and I think they could have made a cute couple if given a chance.
They both wanted to be doctors in the Dic dub I like to think they got married and started their own practice together (although I think Amy wanted to be a pediatrician and Andrew wanted to be a surgeon?)
The real reason for Neo Queen Serenity's seemingly eternal youth was she had Andrew on tap as her highly skilled plastic surgeon. Meanwhile, Amy stayed Crystal Tokyo's most successful pediatrician by secretly disrupting every child's natural aging process, which is why Rini was a nine hundred year old kindergartener.