This My tip is that you visit both parks, even if you only have one day available for Disney, as it is always better to do a little bit of each than to do just one.
Now if you have more days available and fit in your budget I suggest that you stay for at least two days in one of the Disney hotels or one near by.
So you can visit the two parks with much more time and enjoy even more.
To visit the main attractions without the long wait you can book a Fast Pass. The value of Fast Pass varies according to the date of your visit and the attractions you want to avoid the wait, the value goes between€ 30 and€ 150 per person.
To learn more about Fast Pass click on the link below: