There are many wrong answers to this question. Some of them include saying things like, I hate my job, I hate the company, I'm not appreciated there, I hate my boss, I'm sick of working there, etc. Basically, anything negative is a bad answer. If you say something negative, they will think you will eventually get into that situation again while working for them. So I highly recommend you have a good answer that leaves a positive impression while displaying good traits.
This answer shows a couple of good traits. It also shows excitement and mentions the company name. It is personal and direct. This is a generic answer so you can use this if you want. If you decide to think of your own, make sure it displays good traits and the reason for wanting to leave your current job is not a negative reason.