I have a 2015 CX-5, what octane gas should I use?

Hi everyone, I've been lurking for a while now, and I just got my new(used) CX-5 for my 16th Birthday! I'm really happy about it, but my one question is what gas should I put in it? And what are your experiences with different octanes?

Here in Denver we have 85,87, and 91(?). I was just curious performance wise, and if getting higher octane gas is worth it. And there is also the gas mileage question as well.

I really appreciate the help, and if there is something I did wrong with the sub's rules, then please let me know!