Which arrondissement works best for me

Take a cab

Hopefully one of the forum's Paris residents will answer with details, but the metro and pub-trans in Paris is quite extensive and there will be transfers. If that is a concern you should probably taxi.

The metro/train system is great for getting around the city in general - while you're sightseeing and all that. However, I just call a taxi when it comes to transport to the airport. If you're young and strong (which I'm not!) you might be okay with hauling your luggage up and down stairs in metro stations and on and off the trains with various transfers, but for most of us it is worth the cab fare to get to the airport with all your luggage with the least possible stress.

On my last trip to Paris, I booked BT Transfer from CDG to our hotel. There were four adults and the driver was waiting for us after immigration, he had a large van and he sorted the luggage. Used BT transfer as well when leaving Paris (by train). Have booked BT Transfer again for my Paris trip in August. They have a website where you book online and you will receive a confirmation email within an hour. Payment is on the day - card or cash.

Do not use a service like BT transfer.

A number of years ago, Paris instituted a fixed-rate fee for taxis between the airports and the city proper. A taxi from Orly to your lodging in the 15th will cost 36€. No need to tip.

Another option would be to stay somewhere in the vicinity of the Gare de Lyon. The Gare de Lyon is a direct right on the new, automatic line 14 from Orly airport, so you could go straight there without any changes - just the walking once you got off the metro at Gare de Lyon. Then you would be well positioned for your departure, too.

There isn't really a two-day pass in Paris (it's a real shame actually). Well maybe the Paris Visite, but it is usually overpriced.

You could just pay 2€ for a Navigo Easy card, then load trips on it. Attention, if you do end up taking the metro into the city from Orly, only put the airport ticket onto it at first - then add the other regular metro tickets once you are in the city. For some stupid reason, they designed the damned things where they will not hold both an airport ticket and regular tickets at the same time.

Thanks for the input everyone. It sounds like what I was thinking, to use the metro (with the navigo pass) to get around while site seeing, but a taxi to and from the airport and train station will work out well then.

If you don't already have it on your phone, download the Citymapper app for transit info in Paris and many other cities. Extremely useful with detailed info on Metro and buses.