I am assuming that by model style, you mean the execution mode for the virtual service. The VS Model Style really depends on the requirement. For Load and Performance testing, model style determines where we fetch the response from under certain conditions. Other factors such as the capacity of the service, logging mechanism, think time, think scale etc. also come into picture. All these factors determine the performance of the VS.
The more commonly used execution mode for Load and Performance testing ideally should be 'Most Efficient'. In this case, the response time will be under our control. This can be used for cases where you plan on doing load test on application by making the response time consistent by using a virtual service.
Thanks,
Surya.