What are you planning to do on your holiday?
If you're mainly doing Disney and then visiting Paris for 1 day or not at all, then it's easier to stay on site.
If you're mainly visiting Paris sites and visiting Disney for 1 day or so, then it's easier to stay in Paris.
There's a very good train link from Paris to Disney (connected to the main Paris metro, takes about 35 minutes), so it's not too hard to travel between the two places.