Graphner
I wanted to know if the difficulties that Google has created really mean that it is better to buy a model prior to Google Pixel 10 to ensure that GrapheneOS works perfectly.
Right now it doesn't work perfect but it's also not what you'd expect from something being experimental:
You might as well install GrapheneOS on it and set it up now. It's marked experimental because there are USB connectivity issues and some occasional crashes to resolve. You might not want to fully depend on it as a daily driver yet but it's fairly reliable already other than USB. You're treating it as if it's not supported when it is, it's just not production quality yet.
source: https://discuss.grapheneos.org/d/25099-pixel-10-experimental-support-for-grapheneos-is-now-available/642
Maybe you'll also find the GrapheneOS project's recommendations helpful:
We strongly recommend only purchasing one of the following devices for GrapheneOS due to better security and a long minimum support guarantee from launch for full security updates and other improvements:
Pixel 10 Pro Fold (experimental)
Pixel 10 Pro XL (experimental)
Pixel 10 Pro (experimental)
Pixel 10 (experimental)
Pixel 9a
Pixel 9 Pro Fold
Pixel 9 Pro XL
Pixel 9 Pro
Pixel 9
Pixel 8a
Pixel 8 Pro
Pixel 8
8th/9th generation Pixels provide a minimum guarantee of 7 years of support from launch instead of the previous 5 year minimum guarantee. 8th/9th generation Pixels also bring support for the incredibly powerful hardware memory tagging security feature as part of moving to new ARMv9 CPU cores. GrapheneOS uses hardware memory tagging by default to protect the base OS and known compatible user installed apps against exploitation, with the option to use it for all apps and opt-out on a case-by-case basis for the few incompatible with it.
source: https://grapheneos.org/faq#recommended-devices
Choosing a device depends on a number of factors (budget, software support, camera, battery, display, and other features, to name just a few coming to my mind), so it's difficult to give you specific advice.
Purely anecdotal and personal: My Pixel 9 Pro was stolen and I needed a replacement quickly. I wanted a 9 Pro, but was able to buy a lightly used 10 Pro for less money – I installed experimental build from day 1, had only minor issues and haven't regretted it so far. If i wouldn't care so much about cameras, I personally would daily drive a 9a.