how to selecet a appropriate virtual server

It depends on your use-case scenario.

Generally, if you just want to pass through F5 and access servers/resources behind the F5, the Forwarding(IP) VS is a good option.

For load balancing based on Layer 7 information, use Standard VS. When in doubt use this as a default option for load balancing.

For load balancing that is based on Layer 4 information, use Performance VS.

Standard, Performance and Forwarding are the main ones that I have utilized. May be you can use this as a starting point and figure out your relevant use cases.