Love triangles are some of my least favorite and most favorite things in the world. 

Least favorite: I hate it when you're expected to take love triangles seriously. I detest romance in books when it's treated as something normal or something we're supposed to accept. I think it's absolutely absurd, boring, and disgusting to read. I hate love triangles.

Most favorite: That being said, I like romance when you're not supposed to take it seriously. When it's ridiculous, comedic, and way out of scale, I love love triangles. For instance, I think A Midsummer's Night's Dream is hilarious. Last year, I made a ton of love triangles about my friends, including one thing that started out as a love sigma (it looked like a sigma) and quickly grew too large to fit on it's one piece of paper. I ended up writing a five page short story about it which I still find funny to read today. 

That's kind of confusing. Essentially, I don't treat romance as anything serious and I like it when others reflect that view. 

I don't think that love triangles always take away from stories. In some dystopians, yes, I do believe they do, but I usually feel that's more of let's kiss and look at each other meaningfully for long periods of time while zombies surround us. There are times when the characters are in immediate danger and should be focused on surviving, not hashing their feelings out. And yeah, it's usually a girl choosing in between two guys, but that's because the authors of those stories are typically females writing (and this is what I think happens, not what I know for sure) for a young female audience. And yes, both males are usually attractive in one form or another. But I have developed a theory: the best friend never gets the girl in these situations because he's the best friend. A story is about going on an adventure, crossing the threshold, entering a new world, and that's where the broody mysterious hot guy is found. The FMC is attracted to him because he's different, he's part of something that has changed her perception of her world, and that's interesting. The best friend? She's known him, usually for a long time, and he symbolizes safety, he's what she knows and understands, but him? He's part of her old world, and even though he might be drawn into her new world because of her, she's changed, and he hasn't changed with her. A story is about change, after all. It is a struggle to choose for the main character, because she's choosing between safety and her past world and danger and her new one. In the end, though, she's going to choose the new world (even in the rare case she doesn't choose the brooding new guy) because what sort of story would it be if she walked out the door, saw a dragon, and promptly turned around and walked back in? And yeah, I, like Olive, am totally jealous of FMC's and their love interests. (And I totally agree with you on the Iron King.)

Slight spoilers for the Iron Fey  and Mortal Instruments series:

While Puck doesn't turn out to be a human at all, he's still Meghan's best friend, still part of what she sees as safe and familiar. She sees him in a different light, but he's still the boy she's best friends with, someone she isn't afraid of. Simon is the same- even if he ends up being dragged into Clary's new world and turned into a vampire, he's still a part of her old world- in fact, I'd say he's a large part of what she view as he old world.

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Insta-love. Instantaneous love? No. Instantaneous possible attraction? Yes.

And that's all I have to say on this subject because I have to go to bed now.

Insta-love, in my opinion, is (if you think about it) based solely upon a person's appearance. There's no real depth of character to get to know before you decide that you love this person. I can see having a crush, because those are as rare as rocks. Just ask your nearest middle-school girl. This is why I believe that Romeo and Juliet is more of a satire than a romance, because Shakespeare wrote many works detailing healthy relationships that work and are not based entirely off of appearance. It's really shallow, actually, to think that a strong relationship can be based off of physical attraction alone.

I'm not one to diss "sparks" being thrown around, because that's a valid thing to happen - you meet a person and feel a bit of physical attraction. It shouldn't only be physical, though. I rarely read YA books anymore because I feel like all the MFC concentrates on is the DLI's rock-hard abs or deep soulful eyes or whatever. There are very few factors that go into having a real relationship.

On the subject of love triangles: Those don't actually exist. I have yet to see a real-life example of two people being in love with the same person on a level that qualifies as actual love and not just infatuation or idolization. And to have the person love both of those two people back at the exact same level? Unheard of, except in YA lit.

Aside from the questionable believability of it, unnecessary love interests or triangles are just cumbersome and serve as a poorly-thought-through subplot, unless of course you thoroughly thin kthrough your romantic subplots.

Let it be known that I am not immune to romantic subplots. MITWITCH has one. But it is a preestablished relationship and it shows the actual ups and downs of real relationships. LaFaSiB has a prime example of a guy idolizing a girl who is not interested and has her own arc and story after she's established as unavailable. Both of the stories have an actual directive, too - Iggy has to get out of the House-on-the-Hill without getting stuck there for several centuries in LaFaSiB, and Cass and Scooter have the whole figure-this-crazy-stuff-out-before-we-implode thing.

My one work that can be categorized as "romance" is Live Wire, which is a comic about dragons and monster bunnies and random other worlds and fascism and stuff. However, "VioletxJack omg FEEEEEELZ" does not dominate the story. Aforementioned dragons are accidentally introduced to aforementioned random other worlds (that happen to be fascist).

TL; DR Make it believable. Also, have an actual story aside from romance.