This was not about my career as contractor. It's what I saw how employees were treated. As I said some small companies are great and offer great opportunities but there are plenty that work their people to death, miss payroll, pay low salaries in exchange for a big dream that in most cases will never come true for the regular employee.
I've had a year of productive work thrown away by a clueless and arrogant founder that didn't understand the product he was trying to build and the market and was blaming everyone but himself. So you can have the crazy overtime and the bad management that waste it all.
It's not really a question of big and small. Most companies are badly managed (or I am very unlucky). I found in big companies they at least know that making basic efforts to keep employees happy is profitable long-term.
As a contractor you have essentially already taken a deal where you get paid a premium but have no expectation of career growth.
If you have no expectations of career growth at work then big companies are fantastic.