I'm not yet an XS/Max owner, but soon. I read through most of the comments, good input all around. Yes, I'm not too keen on the Intel-only radio, and yes I'd read the WiWavelength post a couple of days ago but I'm not going to be swayed by an anonymous poster with only 6 posts in roughly 7 years who has popped up after 5 years of nothing.
On the other side, none of my friends who work in the field with wireless networks never made it to the football/fútbol parties this weekend - they're busy balancing network loads for the millions of new iPhones and the related IMEI/ICCID/MEID numbers that were crammed on to their networks pretty much overnight. They all hate this time of year now. I went to a nearby Costco to buy my Max, but their registration portal was down (again) and it had been mostly down for around 3 days, so I'll wait until later this week.
Also, the modem FW has been updated with 12.1B1 as of this morning. I've installed it on a VZW 6S+, VZW 6, and ATTWS 6S - I have identical versions of the latter two in my company on iOS 12 or 10.3.3. The newer modem FW has really helped with network connectivity since Friday, when connecting to VZW or ATTWS was a PITA. The ATTWS FW is 33.2 on iOS 12 and 33.5.2 on 12.1 with VZW going from 33.1 on iOS 12 to 33.5.4 (my PRL remained unchanged at 15576 but that's likely irrelevant to most VZW users as I'm still on the old UL Nationwide plan).
I'm not doubting anyone, and I'm not piling on to anything. The newer modem FW has got my devices working fine again. My GF is in the UK visiting family with her new XS being shown around, getting on 12.1 herself has helped out not getting cut off twice during a FT voice call over cellular.
I'm waiting a few days for the networks to get balanced somewhat. The only cellular device I own that's still performing well is my ATTWS Netgear MHS, and it's connecting to the rarely-loaded Band 66. I certainly hope that the new baseband/modem FW and network backend work that's inevitable at the iPhone release fixes this for all of us...