I was always rather partial to round four. The parallel alliances, coupled with the practicality of defence that round (as opposed to say this one), really boosted the number of active players PA had and started a trickle-down effect in terms of quality. The politics were interesting as well with NoS trying to actualise quantum mechanics in alliance politics (can't tell who nos are allied to without observing them which means they'll change their politics so you can never tell who they were originally alied to
)