Heretical notion, but hear me out...
I might actually delay playing this the first couple of days, and instead play through Legacy of the Void's campaign. Blizz games tends to be very well polished, so doing that for a couple of days and giving Bethesda a couple of days for emergency patches might be a good idea. Besides, if I start FO4 I'll be playing that exclusively until I've maxed out a character, finished the story, explored the entire map and so on, which basically means I wouldn't get to LotV for a month or more. On the other hand, LotV will have a very finite amount of gameplay, maxing out at maybe three to four playthroughs at most, as I couldn't give a toss about multiplayer.
Hmm. Yeah, I think that'll be the best way. LotV campaign first, once, then a FO4 playthrough, a second LotV playthrough for breathing room, then another FO4 playthrough etc.
... good grief, having to strategize your gaming? Publishers, get your shit together and stop releasing things on the same day.