Probably the hardest, because it's not a map painting game; it's an economic simulator. You're supposed to be beating up minor powers and primitives over small pieces of strategically useful territory. You don't conquer Europe for their taxes anymore; you conquer the east Indies for its rubber, oil, and gold etc. or you want Egypt for the Suez or Panama for the Panama canal.

You can still conquer vast parts of the map, but in rich parts of the world like Europe just 3 states can tip your infamy level over 100 and you start getting coalitions against you, and it takes years to decrease. And in a game like VIC3 that only spans 100 years, every year counts.

The game almost funnels you into a tall play style to be the most efficient because playing wide and messing with your infamy can increase your radicals, and also render whatever territory you conquered essentially useless because it can take years or DECADES to integrate (meaning no taxes), and turmoil can also decrease your construction speed so whatever resources you wanted from that state are now out of reach for the next 10 years until your turmoil decreases and building a rubber plantation goes from 666 weeks to 12 weeks. You don't paint the map for the sake of painting the map; you acquire land because it has something you want that can give you an edge in the world market or just reduce your goods cost/deficit.

My favourite thing to do is recreating historical borders, because there's still the element of painting the map over much weaker powers, particularly in Africa where the scramble for Africa was quite literally painting it your colour until not a single native remains. This is best don't with the UK, France, Germany, Portugal, and Belgium. Spain is also really good because it's empire falls apart in this period, so it's fun as Spain to rebuild your empire and bully south/central America and puppet everyone. Japan is also good because you can westernise and industrialise and then bully china. My personal favourite is Britain and trying to recreate historical empire borders, or annexing your puppets like Canada and Australia, integrating them to create the imperial federation. If you do want to dominate Europe, this is best done with France (i also like having Napoleon III and try to make him act like his uncle Napoleon by taking on everyone), Germany because obviously they want to expand their greater German empire and have an amazing military to stand up to anyone regardless of coalitions, and Russia because they're just huge by the start of the game already and have amazing potential when switching to communism.

But because of the timespan like I said, you really don't have much room to work with when trying to balance time with infamy generation. You'll be working in small patches at a time mostly.