What is the best way to increase "score" ?
I mean: PVP, Arena, FG or something else ?
Can someone explain me how it works ?
Plat is the fastest way to increase score, mainly because just a single win can net you high score. Second, maybe Gold or FG, then AI4, Silver, and AI3. Bronze generally does not change your score, or even lower it instead.
Of course, the best way does not necessarily mean the fastest way. Plat farmers have somewhat low winrate if you don't want the frustration of losing. AI3 is generally still regarded as good score source, from grinding those easy elders using upped deck or EM deck.