Best opening for 750 elo games ?



Neither of these statements is even remotely true.
This is your last lost game:
https://www.chess.com/game/live/121769660794?username=beechy111
You came out of the opening okay, then you immediately blundered away a piece.
The game before that:
https://www.chess.com/game/live/121769415268?username=beechy111
The same script. The opening is okay, then you blunder a pawn and a piece immediately.
Another thing that is common in both games is that you played way too fast. In a 10 minute game, you played 90 moves in less than 4 minutes. That means that you play semi-random moves extremely fast, and they are often blunders.
Slow down, use your time, think of your moves. That's the only thing that matters. A new opening won't help at all.

Hyper-Nova, there are no efficient openings to play chess at 750 level the main point to play gambits, kings gambit or scotch is to get open and tactics-full game. Person at 750 should learn how to calculate moves, how to think in advance for several moves.
Ok, issue with kings gambit? Go to Italian. Very mainstream but it’s very deep and can be played up to any level.