Well, I looked and didn't see a thread like this so I'm going with that one doesn't exist.
That said the title says it all, which game is your favorite be main series or a spin off and why?
I'm in a 3 way tie with Emerald, Platinum, and PMD Explorers of Sky. Emerald was my first game I played extensively, Platinum renewed my love of the series after a brief hiatus and raised my first lvl 100, and PMD:EoS has the feels. Seriously, who didn't cry when you beat that game?