About two months ago, I got an XS Max and am happy with that. It replaced an iPhone 6S. In physical size they are almost exactly the same. The screen on the XS Max though is closer to the edge.
In most ways there was little reason to upgrade, and I didn’t for a long, long time. Their basic functionality is pretty comparable. The XS Max obviously has all the latest bells and whistles. The speakers for music etc. are also noticeably better. The screen size isn’t all that different (it’s longer), but I use the phone a lot for reading, including Kindle and iBooks. For that reason alone the bigger size makes more sense for me, than the other iPhones you have listed.
At the same time I got a new, cheap (relatively) 9.7 inch iPad Pro to replace my iPad 2, The speed and basic functionality of the old iPad was dropping off a lot. I haven’t bought the iPad pencil yet, which it supports, but I will. Neither do I have the wireless ear buds yet, which can be used on both the XS Max and iPad. I had thought about getting an iPad Mini for reading (as it is bigger than the iPhone), lying down, but its current speed relative to the 9.7 inch model wasn’t anywhere close. And discounted the 9.7 inch was the same or cheaper. I don’t need a lot of storage on either the iPad or iPhone.
One thing I really liked about the iPad is a much larger selection of keyboards and accessories, due to a much bigger market (same physical size as many or most of the older iPads). On the larger iPad Pros, the keyboards looked expensive and from reviews like they often go bad. And not a huge selection. The keyboard I got was cheap, wasn’t at the time listed anywhere as among the best (as it is now), and quite functional.
I had been planning this for awhile, for what the functionality will be (including my best set up, for example, for PDF markup, storage and the best markup tools, which I could judge largely from my older iPad and phone).
To my pleasant surprise, iBooks did a major upgrade while I was looking into all of this, which makes it much more useful to me. The iPad isn’t a PC replacement, but close, and I can do some things with both the phone and the iPad that I didn’t anticipate before buying. And some things you can’t do on a PC.
To dmclone’s point, I expect to have both of these for probably quite awhile before I upgrade.
And if I do, say, to a bigger screen and likely much more expensive iPad (or rather perhaps when I do) I will already be using the most advanced features as long as my current iPad supports them. I’m not sure though that I don’t prefer the smaller size.
