Hey! Another Spanish guy here! Community is increasing!
Gold Saucer is a good one. There's where Cloud and Aeris have a walk... I like Nibelheim too: the Shinra mansoin and the basement (where you meet Sephiroth again and Vincent melody is played).
So...
1. Nibelheim
2. Gold Saucer
3. City of the Ancients (I like its melody as well)
4. Junon harbour (incredible view of the canyon)
I think these could be representative for me... though I liked all the other too.