EU4 - At the moment, the pinnacle of Paradox. Last DLC's are adding perhaps not "essential" features, but those make "minor" countries to be really enjoiable: there are a lot of space for experimenting . Only flaw: past 1700-1750 game is somehow boring , if are not following a specific achievement.
CK - I rate above CK2 just because the idea of MTTH and the new event mechanism as well as the "dinasty" concept was a serious quantum leap .
CK2 - If would be possible to have a little more "historical" flow of events from the early scenarios, it would be perfect. Last DLC are somehow questionable .
Vic - Pops are another wondrous ideas , just one of the pearls inside this game.
EU2 - I was the "perfect EU"
Stellaris - A lot of feature you think "wow, I want to try this.." and after a while you discover that are pretty useless...

But the game has a HUGE potential to rival with EU4
EU3 -It was not a great start.. later expansions are very good. Fortunately they put it apart, redesigning and optimizing everything with EU4.
VIc2 - A lot of great ideas but.... the development halted too early
EU - old, of course, but was the founder of a dinasty
HOI2 - The only "HOI" game I own. Great game, but you could actually play just the major powers
EU:Rome - A touch of EU2 , a little bit of CK , some unfinished ideas.. Danm you, Paradox! I want Roma2 so bad !!!!