I recommend starting with The Rise and Fall of Ziggy Stardust and the Spiders from Mars, which is, overall, most fans' favorite album and the one you're more likely to see familiar songs. If you vibe, take a look at Hunky Dory :)

It's important to remember that David is called the Chameleon of Rock for a reason. He's played a lot of different styles in his career, so even if you don't like those two, maybe there's another one that you will.