I'd say the PS1. It broke Nintendo's dominance of the console market. It drew the support of most of the big Japanese third parties, some of which made few if any games for the N64. It proved that discs were the future format for home console games (carts only persisted afterward on handhelds). And it was the first console to make a huge breakthrough in Europe, which propelled it to over 100M units sold, something no other console had done at that point since in the 8-bit & 16-bit eras North American & Japan were the only big markets for consoles.
The PS2 was the bigger console sales-wise (even if you ignore the long tail post-PS3), but it mostly just carried the momentum Sony had from from the PS1 and built upon it, to the point where no other system really stood much of a chance of facing it in even terms.
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In accordance to the VGC forum rules, §8.5, I hereby exercise my right to demand to be left alone regarding the subject of the effects of the pandemic on video game sales (i.e., "COVID bump").
