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It's most likely just easiest to either fake for the current era, or whatever era you understand the best and can make balanced cards for the best.

Disagree there; SM cards are boring and have a lot of arbitrary stuff specific to that era that doesn't help you if you try to learn a new one later on. I'd suggest starting with BWXY just because so many resources exist for it. ^.^

Eh, whether or not the current era is boring or not I just suggested it because it's what I imagine most people would be the most familiar with.