Most Aggressive Opening?

A final note on that, if we want to get down brass tacks, I have always seen e4 as the most aggressive opening move, because it thrusts an unguarded pawn into the center, opens diagonals for the bishop and queen, and therefore immediately challenges the opponent to decide how to respond to the threat. As Fischer said, e4 is "best by test" in that regard. Flank openings like c4 are also quite aggressive because they allow the opponent to build pieces in the center while developing a strong counterattack on the flank. d4 is more passive, imo because it safely puts a pawn in the center, the queen defending it from any real threat of capture, and therefore giving many options for the opponent to sit back and develop.

Thanks for the answer. I've played some Queen's Gambit games that back up my remark, and some that go against it. In the end, I suppose I'd place the Queen's Gambit somewhere between passive and aggressive.