You’re already over 1600, so you must know by now there is no confirmed “best.” There’s just many mainline solid openings and you’ll do best with the one you are comfortable playing.
Best d4 opening
Best can be properly defined within some subjective context. It's just a question you have to answer for yourself ultimately, maybe with the help of others but at the end of the day you answer it.
I would reach d4 positions via 1. Nf3, not d4 on the first move. That way you get to play many other interesting lines, like the Reti gambit. OR I would play the Trompowsky, to avoid a whole slew of systems.
What is the best d4 opening?