My wife and I arrive at Orly airport on Friday night in early July around 18:40. We need to go to a hotel at the Gare de l'Est. We will use public transportation later that night as well.
Saturday-Tuesday we will be using the public transportation likely only in Zones 1-2, but a lot of usage. Wednesday morning early (the 6th day), we leave our new hotel at the Pompidou Centre to go to CDG airport.
Should we buy a Decouverte card to use Monday-Wednesday and Daily add-ons to our card for Friday-Sunday, or should we use the Navigo Easy Card? It looks like we will need to buy two different cards to cover the 6 days with airports on either end. We can and may take a taxi from Orly to the hotel if that makes it easier.
Thank you, and I will donate.
A Navigo Easy with a combination of tickets (that I'll explain below) appears to be the best option for you, but unfortunately it's not available for purchase when you arrive on Friday at Orly since the Orlybus ticket window closes at 18:00.
So for your first night, I'd suggest buying a Ticket Mobilis day ticket (paper, coupon style ticket) from either the Orlybus ticket machine at Terminal 4 bus loop or from ticket machines at the Tram 7 station, also at Terminal 4. You would need a 1-4 zone Ticket Mobilis costing 14€ per person to cover Orly to Paris (Orly being in zone 4). This will cover you for the Orlybus from Terminal 4 bus loop into Denfert Rochereau in Paris. From Denfert-Rochereau you can transfer to Metro line 4 in direction Porte de Clignacourt until Gare de l'Est station. (If you have lots of heavy luggage and prefer to avoid stairs in the Metro, then Bus 38 will also get you from Denfert Rochereau to Gare de l'Est.) Afterwards you'll be able to use the Ticket Mobilis for other transport until midnight. Note that you can use Tram 7 + Metro 7 to go from Orly Terminal 4 into Paris if you prefer, but it won't be as fast as the Orlybus I don't believe.
For Saturday, Sunday, Monday, Tuesday, if you're planning on using bus, Metro, RER or Trams, with at least 4 one-way trips per day, then it does make sense to buy the Navigo Easy pass (2€) and load it with Navigo Day passes with 1-2 zone coverage for each of those days (8.45€, each day). You can only have 2 Navigo Day Passes on a single Navigo Easy pass at any one time. So you'd need to buy the Day Passes in two separate purchases, one transaction on Saturday for Saturday & Sunday day passes, then on Monday for Monday & Tuesday day passes on Monday.
For Wednesday to get to CDG from Georges Pompidou, you could walk to Chatelet les Halles (it should be very flat, no hills) and purchase a single-use paper ticket for the RER B to CDG. The Navigo Easy cannot be used for RER tickets, so unfortunately it's not useful here. There are escalators for the descent into Chatelet les Halles station and at CDG so you won't have to navigate any stairs like in the Metro system.
The other option to avoid walking to Chatelet les Halles for the RER B is to bus over to Opera Garnier and take the Roissybus, but this will require a bus ticket for the bus over to Opera, the the Roissybus ticket from Opera to CDG. There are no transfers for a Roissybus ticket so you can't buy a Roissybus ticket from Georges Pompidou and use it on a regular city bus over to Opera. If you decide to go this route you can add both the regular bus ticket and Roissybus ticket to your Navigo Easy cards. You can add the Roissybus ticket to your Navigo Easy card at any time during your trip and it will stay there until its validated on Wednesday when you board and tap your Easy card onto the card reader onboard. You don't have to buy Roissybus tickets on the same day of travel.
I hope that answers your questions, Charles. Hope you have a great trip and thanks for the support.