Microsoft, easily. Nintendo are on far stronger footing than previous years and likely have both Smash Bros and Pokemon launching this year. Sony are still the clear market leader and similarly to Nintendo, have a slate of guaranteed hits coming up.
Microsoft have done good work improving Xbox One, but they still lack distinctive, killer software, and are struggling (globally) against PS4 and now Switch. They need to come out swinging and don't seem to have any major cards to play right now - so confirmation of something like Halo 6 or other major exclusives is more important for them. Sony and Nintendo are likely to hunker down around the exclusives they already have as a way of cementing their current momentum; it's Microsoft who need to swing the pendulum in their favour.