Some of my favorites:

Root: Vagabond: I enjoy how this is such a different style than the other three in the base game.

Gaia Project: Ivits: Just very clever encouraging to make a close nit Hivemind rather than spreading out, it's very satisfying every time you hit a new federation milestone.

Scythe: Polania: I just like exploring and claiming as many encounters as possible around the board.

Terraforming Mars: Ecoline for Solo Play: The extra plant just is a load off for my solo games where I don't always have to worry about focusing on oxygen so much and Ecoline feels like I have more freedom over what cards to pick.