chess opening on which you can blindly believe without seeing opponent rating
Just play normal and sound openings against players of any rating. That means you can play a lot of different openings. As White you can safely play at least 1.b3, 1.c4, 1.d4, 1.e4, 1.f4, 1.g3, 1.Nc3 and 1.Nf3 - and maybe also others.
Just stay away from dubious gambits where you loose when your opponent plays the right moves.