The best Chinese language school...

....would have to be That's Mandarin. Their teachers and support staff look after you extremely well and will tailor the programme content to match your needs. All you need is a goal/or goals.
Teachers will only speak Chinese, and although this can be daunting, it helps a lot. You can feel confident the next time you hop into a Beijing taxi and want to navigate beyond "where are you from?" with them.
I highly recommend this school to anyone who is considering taking that step into learning Chinese.