I don't think steam is a good option. I've heard that you need to put down $100 just to be considered by them, and then your game gets pitted against a mass of others to see which one users prefer and gets voted in.
It would be crazy money if you actually got your game on Steam, but you need to have either one hell of a game or just stupid blind luck, combined with a pre-existing mass of followers who use steam and can help vote it in.
On top of that, I don't know if they even accept HTML5 games. Though if they don't, that would be horribly ironic considering they accepted Construct 2 onto it.