Here are my thoughts on the many relationships of Gundam Wing. In case you don't know, most of the relationships talked about here aren't canon in any way...but boy, they sure are fun to imagine ^_- These are all my opinions, so if you disagree with me, that's alright. If you want to flame me because of what I say, feel free; I will only get a good laugh out of what you say, as flaming someone for simply stating their opinion only shows your own intolerance and ignorance, and therefore, it won't hurt me in any way. Anyway, on with the show!
Gundam boys
Heero and Duo: Heh heh, I just have to start out talking about my GW favorite couple ^_^ I find these two to be absolutely adorable together! Their relationship isn't implied very much in the show, but it is implied in the art books ^_^ Notice how in pictures where Heero and Duo are together they usually look happy (and/or evil, like above ^o^), yet in pictures where Heero is with Relena, he usually has this look like, "Get this bitch away from me!" *Ahem* Anyway, I really believe that these two would make a good couple. Duo seems to understand Heero a lot better than the other characters. He certainly understands Heero better than Relena, as can be judged from her totally irrational behavior during the last few episodes (Then again, isn't she always irrational?). While Relena's all freaking out and trying to get to Heero to tell him things he already knows about, Duo trusts Heero enough to let him do his own thing. I think it truly takes another Gundam pilot (or at least someone who's been involved in battle) to understand Heero. Another thing that makes them a great couple is their different personalities. They say opposites attract, after all, and I think that over time, the two of them could use their extreme personality traits to change each other; Heero could calm Duo down a bit, and Duo could make grumpy little Hee-chan cheer up ^_^ Overall, I think they would be very good for each other, and they make the most adorable couple of the show, in my opinion ^_^
Trowa and Quatre: Well, I don't have nearly as much to say about these two. While I think they're cute together and probably the second most implied couple on the show, I just don't have a very strong opinion about them (I focus too much time on Heero and Duo and forget about these two ^_^;;). I support their relationship, but I can't really think of a reason why. Uhh, their violin/flute duet was really cute ^_^;;
Wufei and (insert name here): This may be hard to believe, being the big yaoi fan that I am, but I don't really support any of the relationships Wufei is commonly put into, such as with Treize, in a threesome with Treize and Zechs, or with Sally. Instead, I believe that he is in love with his dead wife Meilan (otherwise known as Nataku). I think that's obvious from the fact that he named his Gundam after her. Some people may say it's just an obsession he has with trying to prove his worthiness as a husband, but he obviously must have had some feelings for her that would make him have such a rampant obsession. Man, if only they had Dragon Balls in the Gundam Wing world ^_^
In the above relationships, all my opinions are pretty firmly set. I really only read 1x2 fics, and pretty much avoid ones with other pairings, unless it's being done for a parody. Pairing fun: Of the ten possible Gundam boy pairings (Or twenty, if you want to get into the specifics of "seme" and "uke" [top and bottom]), I figured that the least likely couple would be 4x5. Come on, can you imagine innocent little Quatre being the dominant one in a relationship with Wufei? Just imagining those two in a relationship at all is hard enough ^_^;;
OZ boys (and sometimes girls)
Treize and Zechs: This is probably the most implied relationship in the series, the first example being in the second episode when the captain of a ship refers to Zechs as "Treize's boy." The biggest evidence seems to be Lady Une's attitude about Zechs. I mean, she really seems to dislike it when Treize favors him...there must be some reason ^_^ I think these two make an interesting couple, though, as you'll see in my next couple opinions, I don't feel too strongly about them being a couple ^_^;;
Zechs and Noin: I think these two really do make a cute couple. However, once again, it's hard for me to have a really strong opinion about them. This may be because in the series, Noin clearly states her feelings for Zechs, but Zechs never really gives any indication of his feelings for her (Kind of similar to Vash and Meryl in Trigun, which may be why I go for KnivesxVash ^_^). I can't tell if they had something going on when they were in military school together, or if it's just a case of unrequited love. However, I did like the end of Endless Waltz when they go off together...that kind of implies that they get together, doesn't it?
Treize and Lady Une: Hmm, this one's tough to call. I find their relationship kind of...odd. I mean, they say all this stuff about loving each other, but they don't really seem to have much chemistry going on in the series, with probably the one exception I can think of where Lady Une flies into space to protect Treize with the Wing Gundam. Otherwise, I don't really see much proof of their relationship.
In the above couples, the one I probably support the most is Zechs and Noin, with Treize and Zechs in a close second, and the least being Treize and Lady Une. Probably the most unusual pairing of this group would be Zechs and Lady Une, seeing as how Lady Une dislikes Zechs so much (although it's mostly out of jealousy...).
Others
Heero and Relena: Oooh boy, you knew this one was coming up, and you probably know what I'm gonna say about it. I can sum it up in two simple words: WOULDN'T WORK. I'm not just saying this because of my extreme hate of Relena, I truly believe they are totally wrong for each other. Like I said earlier in my section about Heero and Duo, she doesn't understand him. If she did, she would know when to leave him alone to do what he knows how to do best. Claiming to be a pacifist, she knows nothing about war, so why does she try to tell him what to do while he's fighting? And I don't care what Relena supporters say, she is stalking Heero for a good part of the early episodes. When you follow someone around when they clearly don't want you to, that's called stalking, people. When you show up at someone's new school unexpectedly, or follow them to Antarctica, that's stalking. I don't know what psychology class you took, but stalking is not the basis of a healthy relationship. Also, they have very opposing views on many subjects. Observe these quotes from each of them. Relena says, "Peace cannot come from fighting," while Heero says, "Peace is nothing but a result of fighting." Oh yeah, sounds like a perfect match *sarcasm off.* I know I said earlier that opposites attract, but there is a difference between opposite personalities and opposite beliefs. With personalities, people at two different extremes can sometimes help each other change a bit to the other side. Beliefs, however, are much more rigid and just get argued about until neither person can stand it anymore. If it was just one issue it might be OK, but they also have opposing beliefs about God, the methods of war, and how peace should be maintained, to name a few. With all these differences, I don't think they'd be able to stand each other (of course, I don't know how anyone could stand Relena :P). In conclusion, I am positive that these two would be absolutely wrong for each other and would only suffer if they tried to have a relationship (Not that I would mind Relena suffering).
Duo and Hilde: I obviously don't support this couple, but I don't really have much reason besides my main reason not to. The main reason is, of course, that I'm a supporter of Heero and Duo. Unlike in the last couple I talked about, I don't necessarily think they'd be wrong for each other, but I just don't see there being much chemistry between them. It's kind of like the Zechs and Noin thing: Hilde seems to have a crush on Duo, but Duo never says how he feels about her (Hilde even looks a bit like Noin...and Duo has long hair like Zechs...hmmm). Yes, there is that one episode where he kind of pauses and looks after her as she runs off, but notice in that same episode, he gave that same look to the guy who drove off in the truck without taking his money o_O;; I think Duo was just being kinda wistful in that episode, so I don't think that was really supposed to be a "loving gaze" he was giving her (if it was, he must love the truck driver, too o_O). I think Duo and Hilde make good friends, but I really don't see them being in a relationship.