Chapter 5, paragraph 27 has the following quote:

The OASIS [was] beautifully rendered in meticulous graphical detail, right down to bugs and blades of grass, wind and weather patterns.

This might be a solid initial quote to begin talking about the OASIS as a utopia. It explains to readers why people might want to spend so much time there.

Chapter 5, paragraph 25 has the next quote:

Even though it was initially marketed as a new kind of massively multiplayer online game, the OASIS quickly evolved into a new way of life.

This quote might work well because it talks about how the OASIS provided a new way of life. All utopias or dystopias involve having people behave certain ways and accept and follow particular rules and ways of life.

The second paragraph of the opening prologue has this quote:

[Halliday] was the video game designer responsible for creating the OASIS, a massively multiplayer online game that had gradually evolved into the globally networked virtual reality most of humanity now used on a daily basis.

Part of a dystopia/utopia is societal control. This quote might work for an essay that tries to show the OASIS as a form of societal control and/or brainwashing.

Chapter 2, paragraph 37 has the following quote:

[OASIS] was much more than a game or an entertainment platform.

Readers are told very early on that the OASIS is much more than only a game. We aren't far enough into the story to see what it might be, but already the seeds have been planted in our minds that the OASIS could be a form of control over society and people.

Chapter 38, paragraph 48 has this quote:

As terrifying and painful as reality can be, it's also the only place where you can find true happiness.

This quote could be a very interesting quote to use, because it highlights the possible dual nature of reality. Reality contains both pain and happiness.