I'd say to check the database, but you need to look out for transpositions, especially with closed games: 1. Nf3 or 1. c4 can easily end up as a Queen's Gambit in another 3-4 moves.
What is the most common opening?

if i were to guess, based of games id say
e4- scotch or italian
d4- london or QG
cant tell which is more common in e4 or d4
1.e4 of some sorts.