Ecosystem integration.

Another vote for the 13 here. It’s a solid phone. The 11 is the last of the 4g phones, and the 12 is a bit of a lemon.

These days they are pretty much all just minor incremental upgrades.

Buy one. Use it until it’s buggered, then replace it, probably with last year’s model because Apple sell those cheaper.

3GS, 4S, 6, 7+, 11, 13.