...excluding Bungie, of course!!
Mine is a toss up between Naughty Dog & Bethesda.
Naughty Dog (IMO) has the best track record (Crash Bandicoot, Jak & Daxter, Uncharted, The Last Of Us)... but I've spent well over a thousand hours playing Fallout & The Elder Scrolls.
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One of those developers does not fit. Can you spot which one?