From what I've seen Madison Keys has the game but she's a mental midget. The sad thing is the players who actually have the most talent don't have that mental fortitude that we've seen in previous younger champions.
The biggest disappointment is Kvitova who seems to have the skill to be on top but just doesn't have any killer instinct. So until one of those players actually step up and believe they can win it all it will be Azarenka and Sharapova. And if those two falter then I can see someone like Sloane sneaking in because while not the most talented she does hold up well mentally.
I left Serena out because we all know that when she's playing well against the field basically nobody can defeat her. It's obvious she'll win more slams in the next three to four years. However, I feel like she's not the next generation and sooner or later she'll have to retire from competitive tennis.
I feel like then we'll truly see who can completely take over. My guess is Azarenka but Sharapova will be right on her heels.