It'd depend on what I thought of that person's chances, and my own. It made sense for Katniss to volunteer in place of Prim, since she did stand a better chance of winning. It'd make less sense for someone like Prim to volunteer for someone like Katniss. though, of course, in the story the decision was made entirely spur-of-the-moment and not tactically.

^^^ That.

For instance, my brother and nephew would have pretty great chances of winning, they're both badass.