From what I have tested so far I think VPN.ac is the best in terms of features, speed, and price. I use this VPN daily on my Windows computers, android phone, and Netgear R6250 router. What I really like about VPN.AC is that all of their protocols (PPTP, L2TP/IPSec, OpenVPN, Secure.Proxy) are working good in China. They give you access to every protocol available and allow you to connect up to 6 devices simultaneously. No paid add-ons! Some other VPN services make you pay extra to use their protocols that work in China or to connect more than one device simultaneously, etc.
This is the VPN that I personally use 80% of the time. The only reason that I don't rate VPN.ac number #1 on my Best VPN for China page is because they don't have dedicated iOS Apps and their Windows software has a few bugs in it. If I am only strictly comparing VPN speeds then VPN.ac is the best VPN for China. I only rate ExpressVPN number #1 because they better Apps and Apps for more devices.
VPN.ac offers a 7 day money back guarantee. You can get a full refund within the first 7 days if you are not completely satisfied with the service.
The Secure.Proxy extension for Chrome and Firefox is actually a proxy, not a VPN. You can think of it as a mini-VPN or a VPN within the browser. It connects very quickly (usually 1 second) and the connection is fast and stable. I like using this because I can open Internet Explorer if I want to go on Chinese sites (Taobao, Online Banking, Chinese video streaming, etc) and I don't have to keep disconnecting and reconnecting a VPN when I want to go back and forth between Chinese sites and overseas sites.
There is a very nice unofficial and unadvertised feature of VPN.ac. Geo restricted video streaming sites such as BBC, Hulu, etc are unblocked automatically regardless of which server location you are connected to. You can connect to Hong Kong and still watch USA or UK geo-restricted streaming video.
The one main disadvantage of VPN.ac is that they do not have a dedicated iOS app. Check here for tips on using VPN.ac on an iPad or iPhone.
Tips for signing up with VPN.ac
Tips for VPN.ac users
Here are some of the FAQ from the VPN.ac website.