Pop Demand Mod (PDM or more specifically POD) is best in my opinion. I personally like it in how it overhauls migration and changes pop promotion, being best about it. It also has a feature that allows to change resources in province under certain conditions, a thing that I missed so much in base game, especially when as agrarian nation you industrialize and your only option may be conquering North Korea.
HPM is another interesting mod. It adds a lot of flavor and events, but what it does with map is a but too much. A bit "railroaded" too, but the mod absolutely worth trying.
There are other mods, some of which mix features and are edited compilations,but these two are most fun and a number of submods is based on them.
