Wow, that's a good question! Very tough to call this one since both Sony and MS were incredibly arrogant and stupid regarding PS3 and XOne respectively.
I'd have to say that Sony was slightly more "arrogant" (Get a second job, rumble is a 'last gen' feature, etc) and MS was a bit more stupid (everybody will LOVE a mandatory Kinect!, ooh look..voice commands to change TV channels!)
And as others have pointed out, it is a a little more understandable why Sony was over-confident/arrogant given the huge success of PS2, and more baffling why MS thought they could just go off in whatever direction they wanted with the XOne and their fans would blindly follow. I mean, within less than a year MS has essentially backpedaled and flipped on every core design decision of the XOne: DRM, always-online, mandatory Kinect, Live paywall for Netflix, etc, etc. When you've changed course on pretty much everything you had planned for I'd say that's a whole lot of stupid...
