This was hotly debated on another board so I think I will open this can of worms up here too. The most obvious answer is Wrestlemania 13 but is it? Because it all depends on whether you think a heel is a heel because of what he does or whether it is because he is booed. There really wasn't much of a difference between Austin's actions pre and post Wrestlemania. In fact in late 1997 he attacked Jim Ross. I would argue that in 1997 at least, Austin was still an antagonistic heel who happened to be cheered. Part of Bret Hart's justification in turning heel was that other heels were being cheered so there was no point in being a babyface anymore. There really wasn't much difference between the actions of Bret and Austin, in fact Bret seemed to respect authority more. Post Survivor Series (where Austin surpisingly got cheered after beating Owen), Austin became a much more fan friendly figure, playing to the crowd. I guess his biggest "babyface" moment was rescusing Stephanie like a "knight in shining armour" from the evil Undertaker in 1999.
So what do you think? Was Austin ever a real face? Did he become more babyface as time went on?