What is the best opening for 800 ELO players?


It doesn't matter which opening you play as long as you get good at playing it.
I looked over your last proper rapid game and the opening was not the problem.

For white learn some ideas of the English 1.c4 and black play the Sicilian 1.e4 c5 It’s what I do and it has brought me to 1600. The Sicilian is a great opening when playing black for the win and the English is an unexpected at your level (and mine too) and is very underrated. However, even if you do get an advantage with good opening theory, remember your Middlegame and endgame truly determine the result of the game.

There isn’t a best opening, per say, but the Scotch, the French, and the Nimzo are great options I would highly recommend. Technically, according to engine-level theory, the best openings are the Ruy Lopez, the Najdorf Sicilian, and the Nimzo.