Where should I look for a Piso in Barcelona!?

Hola Barcino,
in September I’m definitively moving to Barcelona, therefore I need your help in order to find my “piso”.

Which is the zone you have chosen and why?

I am looking for a quiet zone with at least some trees, and I dislike huge buildings.
Is there any place like this in town?
Where should I direct my search?

Thanks in advance for your help!