There are pros and cons to both. You can do it as a great start of your holiday, or the finale.
What you choose really depends on your energy level at the beginning and end of your trip.
Question time!
- Is this your first visit to Paris? Is this your first trip to DLP?
- Is this a once-in-a-lifetime trip or do you think you will be back?
- Where are you travelling from? International or Europe?
- When will you be going?
Going during the week in February is a whole different trip than a weekend in July.
- What's the plan?
I think you will stay at a Disney resort, giving you 3 day passes for both parks. Do you plan to do it all? Are you a person who loves shows, or are you more into rides?
- Who is in your party?
A solo traveller can do a lot more than a family of five with a mom/dad/2 kids/grandma
- What is the plan for Paris?
All this can determine how you will feel when you arrive in France and how you will move through the city and the parks.
My personal preference with these kinds of trips (did it in Asia) is to do the city first, and then do the parks. The parks are my dessert. By then I have grown accustomed to timezone and climate.
Whatever you do, if you are flying in from an international destination, keep your plans for your arrival day as easy as possible. Don't plan too much.