hi acording to the report of UN the best city for live and most expande city of iran is the tariz city with not boaring trafic jam and modern buildings and standard streets and etc .athis city also is a part of areas free zone .and also this city ihas a perfect weather .
My suggestion is Tehran! Its the biggest city of Iran, has more than 10 million people so you can find every type of people, so its not hard to find friends. I also came to Tehran last week, so if you come here, lets meet up.