I would like to know that which load balance method such as src-ip, cookie or etc is most suitable for load balancing proxy servers such as ISA or Bluecoat. The Proxy will listen to many services - http, https, ftp, and etc. Thanks for the help.
The methods you mentioned are not loadbalancing technics, but stickyness features.
Stickyness is not always necessary.
Now, for caching devices, it is good to always send users requesting a same object to a single proxy, so that the same object is not cached in all the proxies.
Therefore, the solution in this case is loadbalancing with url hashing.
For HTTPs, if you terminate SSL on the loadbalancer, you can use the same solution.
For all the other traffic, I would suggest to start with roundrobin and see after a while if it requires some adjustments or not.