I'm probably going to take advantage again of the 24 month interest-free option from Apple and Barclays.
I pay off the outstanding balance on my current iPhone 12 Pro Max with Barclays - around £380 - then I trade it in against the cost of the new 13 Pro Max. Apple and Barclays take the trade in value off the cost of the 13 Pro Max, thus bringing the monthly repayments right down. I'm currently only paying £25.79 each month and bought AppleCare+ outright, which I'll also be due a partial refund on.
What I don't like about the iPhone Upgrade and iPhone Payments plans is they're spread across 20 months and there's no way to bring the monthly repayments down by paying extra each month - this only brings your payment end date forward. There's no option to pay a deposit either, which the 24 month interest-free plan above does by treating my trade-in phone as a deposit.