I am using basic HTTP binding.
Does anybody know which is the best binding in terms of performance as thats the key issue for our site?
Depends on where the services are located.
If they're on the same machine, NetNamedPipeBinding should give you the maximum performance.
Otherwise you'll have to choose depending on where they are located, if they have to communicate over the internet, interopability etc.
Soledad Pano's blog has a good flow chart to help with choosing the appropriate bindings depending on situation