CDG to Reims

You can take a TGV train from CDG to the Champagne-Ardenne station, which is on the outskirts of Reims. The direct trains take 29 minutes. There are train options with a change that take about an hour.

https://loco2.com/en/journey/paris-charles-de-gaulle-airport-tgv-champagne-ardenne-1nyr0xk?currency=EUR&outbound=undefined&leg=outbound

I wouldn't say that train options are terribly long or limited. There are 5-6 nonstop departures a day from CDG to Champagne-Ardenne (30 min) from which you can transfer to a local train to Reims Centre (12 min).

Alternatively, there are 8-10 nonstop trains per day from Gare de l'Est in Paris to Reims Centre (45 min). Gare de l'Est is accessible via the RER B from the airport and an 8-min walk.

I suggest using either Trainline or oui.sncf (the SNCF's booking website) to search for trains and tickets.

An Uber would seem to be rather cost-prohibitive -- CDG to Reims is 140 km/85 mi. If you buy well in advance you could snag CDG to Reims tickets for €22/person or Paris Est to Reims for €15/person, though be aware that very inexpensive rail tickets are also very inflexible, i.e. they are nonrefundable and can't be used on other trains.

In September we're going to spend the first night of our trip in Paris, and take the train to Reims the next morning. Fortunately, our favorite hotel in Paris is within walking distance of the Gare de l'Est.

We took the train to Reims from CDG after arriving on an international flight. Purchased our tickets on arrival and waited about 45 minutes for the next train. Trip to Reims took less than an hour. I don’t like to purchase time sensitive items in advance, would rather pay a small premium so I don’t stress about being late due to flight delays, lines at customs, baggage snafus, etc.

We also did as the first two posts mentioned. The TGV from the airport to the station outside of Reims, cross the platform to the local train and on to the train station in the center of the city. It could not have been any easier.