Element (probably Black Ops line) for Xs Max, eventually. I am the type who buys a piece of hardware and runs it for it's usable life, so I don't mind spending good money on a really good case. I've had two of theirs prior, they are awesome.
I'll also buy a low cost, "overprotective" case of some stripe to keep the phone protected until the "lifelong" case is chosen. Element cases aren't cheap, but I like to give them time to come out with the variants and see them in the field before I buy. Since I am buying this phone at release (not my norm) the cases are behind the phone when it comes to the best combo of protection/tactility of buttons/look. I want to see what the market delivers in the "serious case" arena before I take the plunge. But Element is the first place I keep an eye on - then watch other opinions and see what's out there.
I'll spend the week between order and delivery digging for an interim/temp case to do the job until that's all figured out.