We compare the expressive power of process calculi by studying the problem of electing a leader in a symmetric network of processes. We consider the \pi-calculus with mixed choice, separate choice and internal mobility, value-passing CCS and Mobile Ambients, together with other ambient calculi (Safe Ambients, the Push and Pull Ambient Calculus and Boxed Ambients). We provide a unified approach for all these calculi using reduction semantics.