Which PS system has the best first party lineup, and why?

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Following on from the "best PS first party game ever" thread, if we set aside third party for a moment and just focus on Sony's own games, which PS system do you consider to have the best first party lineup, and what's your argument for why it's the best?

Note: For the purposes of this thread, this is in terms of original/new first party games, not counting backwards compatibility with first party games from prior systems.