Should I get the 12" or the 14"?
The most important consideration is which tool will be the best fit for your body.
If you're under 5'5", over 50, have shoulder issues, or any concerns about the tool weight, the People's/12" is likely for you. This is an easy to use, friendly tool, more than adequate for most home gardens. The older we Meadow Creatures get, the more we appreciate the ease of using the People's broadfork.
If you're taller, younger, stronger, and want the toughest tool you can get, the Tall/14" may be right. If you want to use all your considerable strength in breaking ground, go for it.
Secondarily, if you're still unsure, consider the task. The People's/12" is terrific for working up established beds, loosening soil around perennials, aerating a lawn, prying dandelions and dock out of the garden. BUT, if you mean to break an acre of new ground, plant a thousand apple trees, or dig up well-established holly, the Tall/14" is the tougher tool that will resist bending even when you give it your all.