I actually hired a few teachers from seriousteachers.com, of the three that I did 2 of them worked out alright. I had also contacted a few in America, Canada and Australia. We were not able to work out a proper timeline but they were real people looking for jobs and as I have kept in touch with some of them I know they found what they were looking for. I have had no experience with any of the other sites you have mentioned so I will not comment on them.
What would you suggest to be the best sites to use if wanting to find a job here in china?