Taxi or Uber from the 7th to CDG?

I would think a taxi would be better since it is now a flat rate to the airport.

You could also use a (shared) Shuttle to CDG. I've used that option several times and it's always worked well. I always ask the hotel to make the arrangements the day prior to travel, and they've always used a reliable service. The drivers have the system worked out with great precision, and dropped each passenger at their respective terminals.

Taxi is still the best choice, especially if you have up to 4 passengers and their luggage.
Uber often adds "surge pricing", which can amount to much more than the official flat rate fare mandated by the City.

We have 6 people with luggage. The Taxi cost $55 to and from the 7th with up to 4 people. Does anyone know how much it cost for a Taxi Van for 6 People to and from the 7th?

You can contact G7 Taxi, https://www.g7.fr/en/, they have English speaking staff & they should be able to help you. With G7 you can call a day ahead and reserve a Taxi. Be at the curb when they arrive. They also have an App for smartphones.

When you reserve the taxi, let them know that it will be six passengers. The extra cost is 4€ per person for the 5th and 6th persons. And the base cost is 55€ from the Left Bank not $55 -- not too much of a difference with the current exchange rate but not exactly the same.

You will have to wait for a mini-van for a minute or two, but you'll be charged only 8 EU for the 2 extra passagers, in addition to the flat rate.

And no charge for luggage, unless you have an enormous amount of it.

In this case, you might have to take two regular taxis at the regular flat rate.

An important fact is that Uber is not allowed to pick up passengers at the airports or train stations. You'd have to be in communication with the driver and try to arrange a pickup point somewhere off site.

Two taxis would cost 62 each thus 104 reserved the night before (which you must do to be guaranteed an airport ride in the morning) One large cab would cost 70 Euro total including the 7 Euro booking fee the night before. Just specify how many passengers there are when you book with G7 and they will send a van cab; they even ask if you want an English speaking driver. The cost for the van is 55 plus 8 for the two extra people plus 7 for booking i.e. 70 Euro the vans can hold up to 7 passengers.

I'm not sure what your lodging situation is, but I was staying at a hotel in the 7th last week and they arrange shuttles to CDG. We took one this morning for 19 Euros per person and our van had room for 7 passengers. It worked out great, except the driver was very upset that I didn't know what terminal my flight was leaving from. Luckily another passenger looked up my flight on her phone.