Currently i am in dilemma for choosing between web services, because once i chose it, it'll be fixed.
You should be able to avoid lock-in by sticking to standard APIs like JAX-RS, SAAJ and JAX-WS. Those are supported by various implementations and you should be able to swap implementations without too much effort if need be.
I need more performance as the number of users will be high.
If you keep your code generic enough that you can swap implementations, then you can perform load
testing against different server WS stacks and see if they satisfy the performance requirements.