Chinese website Chongdiantou has tested a variety of Apple power adapters with the iPhone 14 and the iPhone 14 Pro Max, providing useful data about charging speeds and revealing which charger is the most valuable for fast charging.
The short answer is to choose Apple's 30W USB-C power adapter, which at $39 is the company's lowest-priced charger that can charge the iPhone 14 and iPhone 14 Pro Max at their maximum supported charging speeds of 25W and 27W, respectively. All other higher-priced Apple chargers, such as the new 35W adapter with dual USB-C ports for $59, charge the devices at equal to negligibly faster speeds at best.
The chart below is in Chinese, but it shows that all 29W or higher Apple adapters charged the iPhone 14 Pro Max at 26W to nearly 27W.
While charging speeds for the iPhone 14 Plus and iPhone 14 Pro remain to be seen, the 30W adapter should be the best choice for those devices too.
Interestingly, Chongdiantou found that the iPhone 14 Pro Max can briefly achieve peak charging speeds of nearly 29W with Apple's older 29W power adapter, which was designed for the 12-inch MacBook and discontinued in June 2018.
By comparison, the iPhone 13 and iPhone 13 Pro Max are capable of up to 23W and 27W charging speeds, respectively, according to Chongdiantou's sister website ChargerLAB, so Lightning charging speeds for all iPhone 14 models are largely the same this year ahead of Apple's expected switch to USB-C for iPhone 15 models next year.
Apple no longer includes a charger in the box with any iPhones. For all four iPhone 14 models, the company says users can charge the devices to 50% in around 30 to 35 minutes with a supported 20W or higher power adapter.
Update: Chongdiantou sister website ChargerLAB has shared a video of its iPhone 14 Pro Max charging speed test.