As far as I'm aware, official stats from Blizzard is that the player going first is wins a higher % of the time than going second, despite the coin. I'll try and find the source.
I appreciate your point about coin being stronger in some decks than others - that doesn't change the fact that across _all_ of the games of hearthstone being played, if you go first you're more likely to win than if you go second.
User dtech already found the source for me (: -> https://news.ycombinator.com/item?id=8020232