If you have just one day, I hope it won't be during the weekend, It's always busy during the weekend and the holidays, and you don't want to go in Disneyland Paris when it's busy believe me!!!
So if it's your first time, you just have one day, I think you can visit both parks.
For the Studios, you can use half a day. TOT is the same that the one in CA, Rock'N'Roller coaster is the same ride but it's a different "theme" inside, RC totally worth the waiting, Crush coaster doesn't (It's a great ride but the waiting is too long).
Then the rest of the day in Disneyland Park, don't miss the Phantom Manor, BTM (better than in Florida), Space Mountain (nothing like the others), Indiana Jones (It's a Roller Coaster), Pirates of the Caribbean (Better than Florida again), Alice's Curious Labyrinth, and if you still have time Buzz Lightyear Laser Blast (almost the same but still better than Florida). Don't miss Disney Dream at the end of the day!!