Fall is by far the best, anytime from september to mid-november. It won't be nearly as hot as the summer, but it will still be nice enough to go outside and get some stuff done.
Fall is also when my two favorite foods, sardines (hamsi) and pomegranites (nar) come into season. They are both great and cheap and worth seeking out.
Just as a btw, the leaves change a lot later here than in the states, so if you want fall folliage, try late october to mid november.