What is the best answer for: "Why did you leave your last job?" in a job interview?

I would say that I am looking for new challenges and an upgrade to my existing job.

better opportunities i want to learn different job also. i think learning by experience is the best way in finding a job

 I am starting to feel like I need some new challenges.

I have been thinking for a while that I’d like to work for a bigger company with more opportunities for growth