I play on Pokerstars mainly, although I have an account with Party Poker too.
I usually play sit n go games.
I won a cash tournament on Party Poker too a couple of years ago..... must have been beginner's luck as I haven't won another since
All these big companies are legit.
They are against any form of cheating, colluding or rorting.
It is bad for their image.
They make money from raking post and tournament fees, so the more players, the more rakes and fees.
If it got out that they were involved in any kind of funny business, they would lose players.
They also employ heaps of people to monitor hand histories for any signs of cheating.
Sometimes you feel like someone is cheating when you get outdrawn 10 times in a row, but it eventually turns around!
....let your cards be live and your pots be monsters......