I never felt comfortable spending significantly over $500 on a phone despite easily affording it, so I'm mostly limiting myself to mid-range phones (though my Pixel 7a doesn't feel mid-range at all and I'm very happy with it). But if I had to pick a $700+ phone, I'd pick something that has a track record of providing good software support and future-proof hardware.

The Asus Zenfone 10 has amazing hardware, the form factor is perfect, but the latest shenanigans around bootloader unlocking and Asus abandoning the Zenfone lineup (https://9to5google.com/2023/08/26/asus-zenfone-series-ending-report/), adding to my personal experience with an Asus Zenfone and the almost nonexistent software updates that led to my phone being obsoleted within 2 years as it just kept rebooting randomly, all lead me to cross that brand from the list.

The Fairphone 5 looks really good, but to be honest, it's technically a mid-range priced like a high-end phone. Its Qualcomm QCM6490 is a 2 years old 6nm SoC that's ranked between the Qualcomm 860 and the Exynos 1080 in Geekbench, a bit near the Snapdragon 782G, which in other words means that the Fairphone 5 should feel like a OnePlus Nord CE 3 5G in terms of performance. But obviously here you're paying more for fairness and sustainability (though it gets a bit contradicted by their removal of the audio jack).

I'd wait for October 4th to finally confirm the specs, but from what's leaked right now (see https://lemmy.world/comment/3775773) the Pixel 8 Pro looks really good and has some future-proofing (Wi-Fi 7, 7 years of software updates) which makes it conceivable to keep such a phone for 5+ years, especially as they're making parts available through iFixit (though it's obviously not as easy to open as a Fairphone). For me personally it ticks most of the boxes.