The easiest way is to use PI Integrator for BA and have it output to a text file because it is install, configure and done! It's probably also the most scalable. But if it's just a few tags, I would recommend Powershell Tools for PI System with task scheduler.
Paulhave put together below webinar if you wish to know more about Powershell tools:
PIConfig is another option if you want to output PI data as text.
Check out the example script provided Generate a text file of archive data . This script can be invoked periodically through a task scheduler.
The piconfig utility is a command-line administration tool for PI Data Archive and this utility is automatically installed on all PI Data Archive computers and PINS (PI Networking System) nodes.