Yeah, if I were them, I would be.
I mean, I really dont understand why someone would say Sony had a better quality E3 if not by their personal game taste. The event quality of MS was better overall!
People said MS did not presented any surprise, but I diagree. Scalebound and Phantom Dust were both unexpected, not saying that Halo Collection was only a rumour and got oficially announced exactly how people wanted it to be. And they could have gained more claim if they reserved Forza Horizon 2 announce for the show, but still that was an E3 announce imo, just not a surprise anymore.
On the other hand Sony showed LBP3, what was a great surprise, also a already rumoured title (Bloodborn, aka Project Beast) and more gameplay of The Order, what was amazing, but completely expected aswell. They only showed Uncharted to let the audience more happy, but it wasnt much different from their first reveal, since it was pratically a CGI.
Other then that, what both showed was pratically multiplatform titles, so I would not say that MS or Sony won the E3 by showing them. No Mans Sky was a pleasantly surprise, but I think thats multiplatform, right?
I would say that it was almost equally good. But imho MS had more big surprises and a more direct and solid conference. Sony got some extra claim because of The Order and Bloodborn I believe.