My favorite command is Pxl-Change because:
1: you can use it outside of a program to make pixel art (better than pen, becuase you can erase!)
2: you can use it in programs to draw on the screen with one button for each pixel (like in TI-craft), instead of having 2 buttons (one to turn a picel on, and one to turn it off), or having to use pxl-test.
Commands like Pxl-Change are why I like TI-BASIC so much. Even though it's slow, it's really easy to program in because there are a lot of commands that aren't in other programming languages (they were probably included because if you had to use combinations of other commands in TI-BASIC, it would be too slow, unlike in other programming languages on faster computers)