My "new," secondary device from Swappa should be coming today. Factory unlocked, ocean blue Note 9 512gb. I have been trying to find a Note 9 for the right price and the right condition for awhile now.
Hopefully this will be it as its listed in mint condition. Never bought anything on Swappa so I'm a bit nervous of what to expect.
Personally, in regards to specs, I would prefer the phone to have a great display, at least 8GB of RAM, 128GB of storage at least, at least 4000 mAh battery, and my personal preferred size for a display is around 6.4 inches. I have found that my Note 10+ with 12GB of RAM, 256 of internal storage + SD card support is a really good sweet spot.
The S10+ would pretty much fit the bill for all of those, except for I have always been more of a Note fan because I like having the S - pen around, even if I don't always use it.
I don't really care if a device is old or not, in regards to using the Note 9. I don't do anything too risky on it. And if I do things like pay bills or such, I'll use my Note 10+ since it's still getting security patches for quite some time. I wouldn't go any older than the S9/Note 9 generation though. I am sure Android 10 will still be safe to use for quite awhile.