mom929: It is definitely worth it. Go early, bc one day is not enough to see everything, but it's enough to get an eye-full - and it will take all day. Even with the crowds, the palace is still spectacular (we booked a tour and our tour guide told us that during the height of Versailles the crowds in Versailles were alike to the crowds now - bc they wanted to see the king - so if you want to experience what it was like in the past, at least that is something you can think about! - we took the fact with a grain of salt). And if anyone gets lost, have a designated meeting place. It's easy to get lost in the crowd.
If you want to avoid the long line to get in (you will still have to go through a security line), yes, I recommend booking a tour and purchasing the passport (it's a ticket for all access to the grounds). If you purchase a tour, the entrance for guided tours is to the right after you enter the gate. When you get there, they will let you know when you can enter. Go to the Versailles official homepage to see a map. Once you get to the gardens, the crowds will disappear. And the gardens are worth it!
What's not worth it are: The golf like go karts you can rent. You can only have it for 30 minutes for a set price and then every 15 minutes you have it after that they tack on a charge.
Go on the train. I believe it was 15 euro...The train is a hop on, hop off train (keep your ticket and show it to the driver) and it takes you to the Grand Trianon, the Petit Trianon and Marie Antoinette's garden. But be sure you get back on the train before they stop running or else you'll have to trek it all the way back to the palace-which if you're not used to walking long distances will be excruciating pain for your feet!
Also be aware: Once you exit the palace into the gardens you are not allowed back into the palace so make sure you've seen all you want to see in the palace. And Marie Antoinette's hamlet is being renovated and it's closed but you can still walk the grounds and even if you can't get in, the grounds are still an experience you won't forget.
Bon Voyage!
