I was advised by my guide book and other sources to buy a pre paid ticket before arriving to avoid having to queue. On getting there I found there was only ONE queue for everyone, regardless of whether you had a pre paid ticket or not. The other queue was for groups.
I ended up queuing for 2 1/2 hours to get in, despite arriving early, knowing it was going to be a busy attraction.
There was only one member of staff outside directing people and answering questions and a lot of people were furious at this disorganised way of doing things as they had pre paid tickets too. Even before getting into the main courtyard I had to queue for 1/2 hour as there were only three guards checking bags to get through the security point.
It was such a crazy disorganised way of doing things with no barriers up and relying on people to be honest and not just squeeze into the queue.
Also if travelling by train to get there make sure you get a return ticket because trying to buy a ticket from Versailles station to return to Paris reminded me of the boat evacuation scene in Tom Cruise's War of the Worlds. It was every man, or woman for themselves !