so one isnt better than the other?
Not sure what your criteria for 'better' is?
If its reliability/build quality - same materials/components = no difference.
If its driving dynamics, then one is a high-set MPV, the other is a regular family hatch, so although there may be overlap in ability (in some areas such as ride quality) handling & performance (and therefore economy) will differ.
If its the ability to shift people or luggage, then naturally there is more space in the Scenic.
Consumers place different values on various characteristics - that's why there's a choice, its really just a matter of deciding what priorities match up best for you.
If you are really undecided, I'd advise taking a test drive of both, then take it from there.
Best of luck.
EDIT: Its a bit early for me to be typing - just re-read the title (I thought it had been "What's the difference between a Megane and a Scenic"?). Naturally, its just a re-badging excercise, like when Ford changed the Orion to the Escort Saloon. Renault probably felt the model had a brand-image of its own, and decided to split the product range....
Just call me Homer - D'Oh!