Best way to listen to Mozart is on mute.
The fantasias are his best among solo keyboard works. Everything else in his keyboard ouvre is meh....
Edit: Oh, i thought this was about learning his music. Honestly just pick a complete Mozart piano collection album and start there. All you'll get from these threads are people's ideas of what's good or not. For example some people here think anything Chopin composed that's 3+mins long is boring, so they'd only recommend you his preludes or something lol. Likewise I think Mozart's piano sonata's are boring whereas others thinks they're works of art. You already know who you want to focus on, so why not just go all the way and listen to everything?

But seriously though, listen to the fantasias.
Also if you're also talking about non-piano music, operas=mozart at his best. I'd say listen to all but that's time consuming so I recommend Don Gio, Magic Flute, and Marriage of Figaro. All great works.
Chamber music? Listen to it all. Most of it is quality stuff.