Which one of Apple's 2018 iPad or iPad Pro models should you buy?

Now that the new iPad Pro is available, Apple's 2018 iPad lineup consists of four models: the 2018 iPad Pro, the 2017 10.5-inch iPad Pro, the 2018 9.7-inch iPad and the iPad Mini 4. AppleInsider examines all of the options and explains what is worth looking out for when buying a new tablet.