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.