From Paris to Colmar

You need to take the train from Paris to Colmar. 300 Km/hr (185 MPH) is a lot faster than you can do by road, and a lot more comfortable. Large men can get up, walk around, and fetch drinks for the little ladies.
Once you get there, a car is not good in Colmar (everything is in walking distance), but if you want to go out to the wine villages, a car is a distinct advantage. Hire in Colmar for 3-4 of your 5 days.

What are you doing after Colmar? That may affect the options.
What about Strasbourg? Most people want to visit Strasbourg as well, and you go through it before reaching Colmar from Paris.

Trains from Paris to Colmar do all pass through Strasbourg, but 4 departures per day run direct all the way, not requiring an actual change of trains. For connections at any other time, Strasbourg-Colmar is 30 minutes one way by frequent regional train.

In September 2015 we were four adults (2 tall men) who went from Paris to Colmar. We took the train from Paris to Strasbourg. Picked up a mini van rental car near the train station. Stowed our bags, parked the car and spend the day in Strasbourg. Then we drove to Colmar as our home base for the Alsace region for four nights. It was amazing. Stayed at an eclectic place in RS book that we loved, offered easy parking and access into and out of the city for our day trips.

Laurie,

Definitely take the high speed TGV train on that route, as 300 km/h is a lot faster than any Van. As Chris mentioned, they're very comfortable and you can wander about the train and enjoy the scenery.

Some trains on that route depart from Paris Est and others from Paris Gare de Lyon. You'll have to use Taxi or Metro to get from the area of your Paris lodgings to the appropriate station. With five adults you could also use a pre-booked Shuttle Van as that will accommodate all five plus luggage.

Note that the TGV trains require a compulsory seat reservation, which will be included with your tickets. If you're willing to commit to a specific train, you can pre-purchase tickets at https://www.trainline.eu/ or you can buy them at any station or SNCF Boutique in Paris a few days before you'll be travelling.

Regarding Ken's reply: All direct trains from Paris to Colmar leave from Gare de l'Est. Ken is possibly seeing journeys on websites that involve travelling from Paris Gare de Lyon to Basel and heading to Colmar from there, which might be faster for certain departure times but is more complicated.