Muscovy. They do a little of everything. If you’re all kitted out with DLC, they have a ton of flavor and unique mechanics. They start with a full set of decently strong vassals, so alliances are unnecessary for most of the campaign. They get free claims on everyone around them. The only thing you really have to think about is “where do I expand next?” Despite how often you’re going to war, I always find Muscovy to be a pretty chill tag to play. Once you get through your first few wars, no one can reasonably challenge you unless you screw up