What are the differences and similarities between Julia and Winston in 1984 - what chapters best demonstrate their characteristics?

Winston is older than Julia, and unlike her, he remembers the time before the Party took over. For example, he remembers airplanes from his childhood, even though the Party insists it invented them. Winston is obsessed with historical fact, with the theoretical aspects of the Party, such as why the leadership wants to institute Newspeak, and with the idea of an organized rebellion against Party rule.
Julia does not care about historical facts such as when the airplane was invented. She is practical, sensual, and worldly. For her, the focus is on how to survive as well as she can in the world she lives in right now. She doesn't care about Newspeak or rebellions, but she does want to know where to find bootleg coffee or lipstick.
The two complement each other well. Both intensely dislike the Party and want to create their own world apart from the Party and its surveillance. They both love each other, and both have a capacity for loving human relationships. Both can see through the Party's lies.
It's important to note, however, that while we are almost always inside Winston's head, hearing his thoughts, we view Julia through Winston's eyes and never are privy to Julia's innermost thoughts unless she expresses them aloud to Winston.
The best chapter to find out about Winston and Julia is chapter 5 in Part II. It starts with Syme's disappearance, but if you go in a few pages to where the two lovers are in the room above Mr. Charrington's shop, you should find what you need.