I've been subscribing to Expertflyer for about 18 months I think and I am very happy to use it. I find the website reliable and very easy to use. Also when I've made comments on their webpage they've answered promptly and even changed the website as per my suggestion! All in all, I'm very happy with EF and will continue using it.

I used to subscribe to KVS when you could still make a voluntarily contribution. But since the whole thing with levels came along it is more like a paysite. Ever since my harddrive crashed and I had to reinstall windows (thus losing my registration data and getting a new system code for KVS) I never bothered to reregister.
Still, I would like to thank KVS for developing this tool.

EF is my prefered choice.