Between the Big three (Microsoft, Sony, Nintendo), who is the worst when at the top?

[GaoGaiGarV]

Nintendo, easily.

Back in time when the NES was around they demanded that 3rd party publishers only release their games on the NES in the US which completely ruined the market for their competition.
This kind of unhealthy exclusivity was basically the same Xbox is trying to do now by buying all these big publishers, so Microsoft is most probably becoming the next 80s-Nintendo in the future.