Which openings or gambits are good to defeat 1400+ ELO?

It is not in the opening you will win over +1400. You will have to study middlegame and endgame. And you will have to study your own games and learn from them.

I studied openings and I can tell you that you will win/lose most of your games from the middlegame and endgames. Opening only helps you reach a good middlegame but there is a reason why Hikaru was able to speedrun from a beginner rating to at least 2000 with garbage openings. 

But for reference, I played the Queen's Gambit which gave me an above-average win rate. I still refer back to this study to understand the opening more and find "better" continuations. But you will get a lot more from analyzing your games to see where you went wrong and work from there

Do you want to win? Play unorthodox moves in the opening, never mainlines, never popular openings, unknown gambits, etc. Your opponent presumably won't know what to do against it and should end up losing.
Do you want to improve? Learn sidelines of popular openings and mainlines of unpopular openings (hypermoderns and low theory openings, not gambits), and then play middlegames and endgames. It'll take a lot longer to improve that 100 points you probably want than the first method, but you'll get the NEXT 100 points so much faster. Game knowledge snowballs, and openings (even popular ones) happen so rarely that they aren't worth focusing on until you get to a high enough level or have enough time that you can afford to study them.

Vienna gambit is a patzer killer. ITs one of the rare gambits black shoudnt take (aside from QG which everyone knows isnt a gambit) and its easy to misunderstand the position and try to play it like a king's gambit but blacks counterplay is more narrow here.

The Max Lange Vienna Gambit or the Falkbeer Vienna Gambit that leads to the mainline that Black does very well in?

objectively, probably the queen's gambit. but a 700 probably doesn't understand the theory, and frankly, neither do I, but for me, it doesn't really matter because I always play 1. e4, and I play the indian game when faced with 1. d4.

Schandorff has a good book about the Queen's Gambit. He doesn't focus too much on the theory but he does go through a lot of games to show you the ideas about the position

Agree. It is a very good book on a very important opening with concepts that can also be used in a lot of other openings.

I didn't realize they weren't 1300. That changes things. 1370 peak isn't 1300, and you're currently 700, why are you asking about an opening repertoire for 1400s? Start with the Scotch and the KID, move on to more openings once you hit 1000

I don’t need to learn the QG from either side so I don’t really care too much

I don't play QG either. I plan to eventually, but as it stands my London and Colle are strong enough to cover 1. d4 d5. And as Black against 1. d4 I'll play an Indian or Modern transposition.

The one that gave me a 70% win rate until about 1800 (don’t quote me on that)

The point is, people U1800 don’t usually keep up with attacking openings like the Vienna , and can have a lot of trouble dealing with them, which is good for you. Black doing well in the mainline is because the Vienna gambit gives free equality to anyone who studies it, but finding that ingame without the study? You’ll most likely end up with an advantage U1800 unless someone’s booked up.

If ur under 1500 dont even worry about openings just get your pieces out and develop 

Okay, I'm assuming the Max Lange Vienna Gambit then.

Disagree i would say you should start learning a bit of theory when you hit like 1000 cc

Under 1000 you should at least know one very, very simple opening out to 4 moves for each color, I'd recommend openings like KID (Pirc move order if 1. e4, Modern move order if 1. d4) for Black and Reti (KIA or transpose to Scotch) for White. Once you hit 1000, start learning more openings out to 4 or 5 moves, except the 6 most popular (Indian, Sicilian, QG, English, French, Spanish), and try to learn sidelines, not gambits, solid play, not gambits. From there, try to slowly expand your repertoire, again I'd recommend a mild avoidance of the 6 most popular, but considering that it's kind of out of your control at some points, learn a simple, uncommon line or two just in case. Once you hit 1500, you should presumably have enough opening knowledge that nothing really surprises you, and if it does you'll learn it within a game or two. From there, have 3-4 dedicated openings that you know all the common variations for and the ideas for after the theory, but primarily focus on middlegames and endgames. You should be getting much more even positions without study by that point.  

I think that the Jaenisch gambit will bring you big success. It is really annoying to play against and black is also completely ok according to the engine.