Not to pry but..

How old are you

What do you like to do

Are you coming alone or with friends/family

Phoenix is over 100 miles square.

Tempe in Sept will basically have college kids going back to school

Mill Ave is busy in the evenings - but not much else to do

Public transportation in Phoenix sucks

Do you want to play golf, swim, go see Frank Lloyd Wright Architecture, go up to the Grand Canyon, Sedona -etc

If you give us some more specifics we can helpb