I went to Versailles ~7 years ago when I traveled to France with my girlfriends, but I don't remember much except just how grand and unbelievable it was. My mom was in Paris for the day last Sunday, so we decided to trek out to the palace for a visit. I highly recommend taking an Uber Pop (cheapest car sharing option in Paris) from Paris to Versailles. It will run you ~20-25 Euros, depending on what part of the city you start in, but taking the train is sort of pricy (~4 Euros per person + metro fare to get to the train), so it ends up costing around the same amount if there are 3-4 people. You likely can't take an Uber back, but it's the best and most efficient way to get there! :)
We had an amazing time (I recommend watching Marie Antoinette beforehand to get in the mood :), but it was so incredibly crowded. If you can avoid a weekend visit, do it! Last time I went during the week and it was much more laid back and we got to enjoy it more. The lines and crowds were pretty unbearable. Still, the palace is so ornate and a must see during your trip.
The best part of the day by far was our visit to the gardens. We brought our own picnic lunch (salami, cheese, grapes, cherries, strawberries, a baguette, and of course, wine!), found a bench, and entertained ourselves with some serious people watching. The gardens are impressive and expansive and we had fun wandering around for hours after lunch. Thanks for visiting, Mama! xo