iPhone X from last year will probably retain the most value of the lot I think, everything else is a crapshoot. iPhone 8 should retain value, but in the face of a new 6.1-inch LCD iPhone “X” like offering it could be severely devalued by that.
Also, in my view, if an iPhone has had a 3rd party repair of any kind, it’s basically worthless second hand.
I value phones from AppleTalk slightly higher than anywhere else as I trust the owners to be honest with whether it’s had a 3rd party repair or not.
My wife is due to upgrade from an iPhone 6s this year too - I’m curious to see what the second hand iPhone X market is like in a couple of months. Looking to get her an iPhone X assuming it’s a reasonable price. I’ll see what the market is like and then try to pick one up for her.
I’m actually not that interested in switching from my iPhone 7+ (Jet Black). I’d have gone to an 8+ in a heartbeat if they has stainless sides, but the aluminium is just too slippery. I am caseless, and the jet black finish is a god send for grippability.
I’m always curious to know how many of any given iPhone that isn’t the current model Apple sell. It must be a very specific customer who will buy and old phone brand new but not want to save more by going second hand…