Lithuania with Lions of the North is really good. You open with mil focus to balance your mana spread (since your starting ruler is 4-4-1) and pick Aristocratic ideas first (a near perfect pick for Lithuania), then I like following with Infrastructure and Trade.
You rival Poland and build an anti-Polish coalition to gank them that ideally includes at least the Teutonic Order and either Hungary or Bohemia (Austria will almost always refuse to attack Poland because they're friendly due to mutual rivalries). Go for show strength on Novgorod on Nov 11th while you put your diplomats to work on improving relations. Once you declare on Poland for restore union with your buddies, declare on Livionian Order a month later (since Teutons won't join) and gobble them up first. Within a couple years you've got a very good power base with all the right culture right religion Baltic land from the Livonian Order and Poland subjugated.