Early stage engineer at startups (including a unicorn):
pros: Fun work, you learn a ton, unlimited PTO (if you can actually use it), lavish benefits like free lunch, decent company culture, opportunities to try new things.
cons: Poor work life balance, low chance of a bonus, low equity if any, poor management/leadership, lots of hand wavey bs about being number 1, poor career progression, lots of over selling of what you'll be working on, Chicago isn't big on "cashing out" so most startup equity wont really net you much if anything.
compensation: Average for the market in Chicago, depending on where you land as far as talent and skills you can probably get 100k-200k base.
Big tech companies:
pros: great work life balance, annual bonus from 10-20%, decent career progression, more opportunities to specialize in something if that's your thing.
cons: Lack luster tech, no equity, lots of red tape, lots of mediocre/bad engineers, occasionally have to work with legacy code.
compensation: 100k - 250k base salary based on skills/talent/position.
From my experience in Chicago it really comes down to stability, work life balance, and trust. From what I've seen the big players are usually a lot more upfront about what you will actually be working on day to day and they provide a level of stability that others can not. On the other hand though you can grow a lot more as an engineer at a startup if you put in the effort.