Josette,
Well I have a rather interesting answer for you. My choice would be neither. I would prefer, when dining in Downtown Disney, to go elsewhere. My favorites, which I recommend to you, are;
- Raglan Road
- House of Blues
- Bongos
- Wolfgang Puck's Cafe
There is also a new place called Paradiso 37. I can't personally recommend it, as I have yet to get there since it opened a few months ago, but it features Central and Latin American fare.
But if forced to choose between your two suggestions, I would VERY easily pick Planet Hollywood for a better atmosphere (and quieter one too), and much better food. I just prefer the above suggestions for more creative menus, far preferable atmospheres, and better overall experiences.
I hope that this helps!
Have a magical (and delicious) vacation!