Eh, I'm in no rush for the next generation to come knocking. I didn't get into the new one until 1.5 years into it, and I don't really see myself buying either the PS5 or Xbone2 on day one.
Having said that, it's pretty much garanteed I'll get both within their lifespan, and the first one I get comes down to witchever one has the biggest selection of interesting exclusives, and/or the best support for backwards-compatibility.
Honestly, I feel slightly more inclined to get the Microsoft console first, casue they've done a pretty good job with said BC this cycle - and I have enough games in my backlog to keep myself entertained well into retirement at this point anyway.