Ok, I have used Witopia SSL-VPN for four years and sadly accessing the service from within China is "painfully slow". The service was "ok" from within the Middle East, but never better than just ok.
As a precursor you may ask why is this chap qualified to judge their quality and performance? Well, as a user I can provide my opinion based on my experience and as a professional working with the technology and telecommunications field for nearly 25 years I know a thing or two about troubleshooting network and system problems. Just as some companies in the pre-broadband era overburdened their modem pools today it would seem that VPN service providers are squeezing every nickel in a grab for cash, rather than focusing on service. And I challenge any VPN service provider to "prove me wrong" with a transparent control panel that shows us "the consumer" that the load on their systems "in real-time" are less than maxed out(24x7x365)! This is not hard and any script monkey these days can bash together MRTG and screen scrape it into a control panel. One good coder can make it a real-time data stream using mySQL and php. Prove it!
My testing of Witopis has included the use of the service via a Desktop and Laptop and using multiple wire-line and wireless access services from each of the telecommunication providers within China from a variety of cities.
I would avoid Witopia if you are in China and when I find a provider that is truly worthy of a "positive review" you can guarantee that I will provide one here on this site.