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"1 d4 dull & drawish" - Fischer
1.) d4...is best by test
There are small differences. I think that 1. d4 is stronger than 1. e4 and I've explained why I think that. It's because after 1. e4, it's natural for white to attack, whereas after 1. d4, it's more natural for white to react positionally to black's moves. For that reason, 1. e4 is logically the weakest of all white's main four first moves. That's because chess is a draw by best play and therefore white can't win just by attacking.
e4 for effort
d4 for different