Pawn to e4 vs. d4

If it weren't for the Sicilian Defense... it wouldn't even be close.  e4 would be the obvious pick.

But because the Sicilian Defense exists... do you think d4 is the better opening move?

No, black can equalize against both. It's all a matter of taste.

The opening move you play depends on the style of play.  Just understanding the difference between King Pawn and Queen Pawn games determines the style.  The former is sharper, while the latter is tamer.  Strong aggressive tacticians like Bobby Fischer, Garry Kasparov, and Judit Polgar prefer e4, while tenacious defenders prefer d4.  Tigran Petrosian and Viktor Korchnoi employed the English Opening (1. c4), which would often transpose to a Queen Pawn opening.  The Zukertort Opening (1. Nf3), my favorite, can transpose to either a Queen Pawn opening or a Sicilian Defense.

Saying that Kasparov prefered e4 is somewhat of a lie, since during his career he has played d4 more than e4.