Eight to thirteen depending upon how you count.
My primary devices: 2G,3GS,4S,5,6,6S,8,11P
Bought for family: 4,5C,11,14P
Bought as a spare phone: XS
Favorite is a tough call between my 6S and 11 pro.
6S story:
Absolutely hated the 5 and 6. They were both unreliable buggy garbage. I hated the 6 so much I switched to Android (Galaxy S6). That brief Android foray only lasted about 8 months – when I stumbled into a very good deal on a used 6S I jumped at the opportunity to switch back. The 6S was special because I got back to iOS and it was the first phone I actually liked since my 4S.
11 Pro story:
Bought it new and I'm still using it. The Lightning port has been dead for a year (Qi charging only) and Face ID sensor just died, but other than that it's still doing its job. This is the first phone I've worn out before getting tired of it and upgrading for newer tech. I actually bought a 14 Pro at launch to replace it - but it's still sitting in the box. I don't like the size increase of the newer form factor, but mostly the 11 Pro just kept working well enough that I never felt compelled to take the time to set up the 14 Pro. My partner is finally going to get the 14 Pro this weekend as her 11 is totaled (broken glass on both sides), and I will either get a new 16 Pro or just use the XS I have in a drawer and hold out for the 17. Honestly, the only feature I really care about on a new phone is upgrading to USB-C so I can be done with Lightning cables (which is ironic since the upgrade to Lightning is why I bought my much-regretted iPhone 5).