e4 or d4?

mmm. Both are played by Grandmasters. Whatever opening you think is best, you choose

I tend to play both actually

I prefer e4. it is easier than d4 to do castling. I usually play like this; 1. e4 e5 2. c4 Nf6 3. d3 like this. it is defensive... or 1. e4 e5 2. f4 for remove opponent's E-line pawn and it is quite good.

that was very useful thanks

I'm not sure why I like d4 way better than e4. Maybe I just like the opening selection.

e4 i play because it develops the light squared bishop.

I play neither but if I did I would prefer d4 because there are less replies against it than against e4, who wants to learn ten separate openings and all their lines when playing one opening.