The iPhone Duo is easily the more exciting gadget.
It folds. It opens into a much larger screen. It feels genuinely different from the iPhones we've been carrying for years. If you gave me both phones for an afternoon, I'd probably pick up the Duo first.
But if I had to spend my own money?
I'd buy the iPhone 18 Pro.
The reason is simple. Once the novelty of folding the Duo wears off, I need a phone that works for everything I actually do every day. The iPhone 18 Pro gives me the more interesting camera system, including that new variable-aperture main camera, without the extra thickness, weight and compromises that come with a foldable.
Then there's the price.
The Duo is the sort of gadget I desperately want to play with but would have difficulty justifying. You're paying a significant premium for that folding display, and I'm not yet convinced having a small tablet in my pocket would change my daily routine enough to justify it.
The 18 Pro is admittedly less exciting. Put it beside last year's iPhone and nobody across the room is going to ask what strange new gadget you're carrying.
But sometimes the gadget I want to play with and the gadget I'd actually buy are two different things.
I'd take the Duo on a weekend just to experiment with it. I'd open apps side by side, watch videos on the big screen, try the cameras and probably fold and unfold it far more times than necessary.
Then I'd reluctantly give it back.
And buy the iPhone 18 Pro.
The Duo wins the gadget geek part of my brain.
The 18 Pro wins my wallet.