A switch case would run considerably faster in mIRC script than if/else's because it would evaluate the condition only once, compared to evaluating it up to n times and an additional variable being evaluated n-1 times aswell using the most efficient if/else equivalent (where n is the number of cases). The goto method can just about match the efficiency of a switch statement for simple situations but it is deeply flawed and can cause major issues if you intend to use error handling (not to mention it allows only a single "switch-equivalent" in each scope).
Your example code doesn't allow for cascading which is a defining feature of switch statements.
