Smart Phone - Mobile Communications Central + quick access to any information needed and ability to do common tasks remotely (not sure why anyone really needs to upgrade this more than every 2-3 years)
Amazon Tablet - General Video Consumption Device (we only turn on the TV when viewing family movies these days) that can also be used for decent video conferencing, Also great for some specific android apps that are designed for larger tablet screens, can substitute for laptop for most purposes, especially when traveling light. (can probably go 4-5 years between upgrades)
Phablet - Those who somehow need to take the worst aspects of both smart phones and tablets and combine into one, but definitately a reasonable choice for when one gets older and using small smartphone screens is no longer appropriate.
Computer + Large Monitor - For doing everything else, especially for extended duration. Build it well and it can go 4-10 years between major upgrades.
Laptop - When you are willing to pay double for less performance, substantial reductions in upgradeability, and a smaller screen in exchange for using less space and being able to move a computer easily.