I find Hearthstone to be the least offensive because a) its a CCG and thats how the game is sustainable and b) you can craft the card you really want from the cards you dont want
I think loot boxes make the most sense in the context of a CCG, because random drops encourage unique deck building. Hearthstone's system is less abusive than it could be, but it's still a loot box-based system. It's something I've been on the fence about for a while and this article pushed me over the edge.