The Mirador de San Nicolas offers one of the most famous panorama for the Alhambra. 

The Mirador de San Nicolas, seen from the Silla del Moro
It gets crowded very quickly, by your fellow travellers as well as people trying to sell stuff to the aforementioned travellers. However, when exploring the Albayzin it will be a target worth reaching. 

Note that the Church of San Nicolas offers a view from its tower, which is a little bit better, if you look for that extra picture everyone is looking for. The Church itself is in repair, so the 2€ you pay to climb up will go to the fund for the restoration.