My current iPhone 6s Plus really is the best phone I've ever had. With its super-fast TouchID, Force Touch for shortcuts, optical image stabilization, and super batter life, it truly is able to eclipse my previous best phone--the iPhone 5s.
I still love my old 5s until the end of time, with it's perfect one-handed form factor, and it took me a while to warm up the 6s Plus paperweight. But I just can't imagine going back to the 5s now that my hands have adapted to the 6s Plus.
The 6s Plus truly is Apple's best iPhone yet, and my favorite; and I've had 4 of them over the past 7 years.
The 4S was just a gorgeous work of art, with it's glass casing and modern form factor. And the 3GS was, well, it was my first iPhone and one tends to feel endeared towards their first of anything; but it looks and acts like a dinosaur now.
Before that I had my first smartphone, the Cingular 8125, a Windows Mobile (6?) phone with a little stylus. The photos are pure crap compared to those of today, but it was my first all-in-one; and my Motorola V400 flip-phone was my very first phone at all.