PS5. Why? Because I've already owned the first 4 Playstations, while I've never owned an XBox. There are a lot of reasons for this, but that is just the simple way to say it. Microsoft would have to up their game significantly for me to buy one of their consoles: better games, more reliable hardware, less company sliminess, etc.... On the other hand I didn't really like the PS4, so if the PS5 is similar to that I may not buy one of those either.
Basically I am more likely to buy neither than I am to get an XBox.