drive vs train to Giverny

You could pick up a rental car at CDG or at Mantes-de Jolie. I'd base it on how jet lagged you will be. Also, we had a rental car while in Rouen as part of a larger trip. We found a 24 hour parking garage and just left our car parked while there. It worked out fine.
I liked having a car in that part of France; and it was easy to drive there.

Thanks! Yes we are definitely going to have a car. We plan to go to Normandy, Brittany and the Loire. We'll probably return the car in Tours and take a TGV into CDG. Had toyed with the idea of driving back to the airport but all the reports of car rental return hell convinced me otherwise.

I have returned a car to CDG and don't remember it being that difficult. Maybe I was just lucky, IDK. But keep in mind that returning a car to a different location often results in an extra charge. And if returning to CDG make sure you leave yourself a lot of time to deal with airport traffic. Plus, the drop-off hours may be longer at CDG than some more remote rental office. Always check hours regardless—particularly for pick up (drop-off can usually be done after hours, but document the car's condition with photos/video if you choose to do this).

Drive from CDG to Giverny is a bit over an hour and pretty straight forward after you leave the airport jumble. Google maps works very well there. Rental counters at 2E/2F can be a zoo depending upon arrivals and time of day.

There is an underground garage in Rouen (not cheap?) near the historic district. Pretty easy walk into where you wish to be. It is in Rick's guide.

Many thanks to all of you who responded and provided your input. I've reserved a car with Avis. I have their app and they have my information so theoretically I should just be able to go to their fast track location and my car will be there with the keys in it. Theoretically! I thought long and hard about taking a train out of CDG but we always seem to end up on the wrong side of the tracks and have to haul our luggage up and down the stairs again. I've managed to get out of Seattle, LA, Maui, Bordeaux and other airports in rentals and I can follow French road signs (generally) so I think I will be okay.
I am able to return the car in the Tours TGV station. Did not want to drive through Paris and to the airport. By turning the car in there I avoid the extra hour or two that would result in an added day charge for the rental and there wasn't a significant difference in cost with a different drop-off location. My understanding is that the TVG arrives at CDG so we should be able to find the Sheraton there.

This was my first hurdle in planning this trip. We are going to Giverny, Normandy, Brittany and the Loire so I am sure I will encounter more hurdles.

Thank you all again for getting me over this one.

Driving to Giverny on a Saturday morning will indeed be hassle-free, and the drive from CDG is short enough to be safe after the overnight flight (my limit is 1.5-2 hours).

2 nights is a long time in Giverny proper: make sure to tour the area! La Roche Guyon is not to be missed, and you could easily visit Château-Gaillard in Les Andelys as well.

Since you will be driving from Paris, I second the recommendation of stopping at La Roche-Guyon. Among other things, this was the headquarters for Field Marshall Erwin Rommel when he commanded the German forces in Normandy. It also has a wonderful high up view of the lower Seine River. On my way out of there, my GPS directed me to a small car ferry that crosses the river. Also, on your way out of Rouen, I highly recommend seeing Abbaye de Jumièges. This monastery was founded in 654, but the newer church was consecrated in 1067 when William the Conqueror returned from his successful invasion of England. It is now a wonderful ruin and a fascinating place to wander around. It is also en route from Rouen to the Battle of Normandy sites if you happen to be heading that way.

I second Pharmer Phil about the Abbe de Jumieges. Take the D982 from Rouen there. It is a beautiful drive along the Serine River. You pass through Villequier, where there is a small Victor Hugo Museum. We drove all the way to Bayeux on the D roads. Much, much nicer than the autoroute, no tolls, a bit slower, but well worth it. Have fun! Rouen is a great place to visit, as well!

OOPs! Abbaye, not Abbe! The Abbe would not be a pleasant sight after all this time!

Month of trip? Giverny is VERY crowded in season. But having rented a bike long ago to get from the train station, I'd use the car for your itinerary.

Make sure you check the exact days, hours, and 2-hour lunch hours of the Tours (or perhaps St Pierre des Corps) rental office. Take a screen shot.

I found it to be an easy drive. I would do it again without hesitation.