215/70-16 seems to be the correct size for your Astro, so that would be my choice. I usually prefer to use the correct size over an off-size, unless there is a specific reason for using the alternate size (more/better tires available in the new size, minus-sizing for winter, etc)
Hankook makes many different tires, some of which last longer than others.
It also depends on what off-brand it is, who makes it, etc. For example, Walmart's Douglas tires are made by Goodyear, and plenty of off-brand tires are made by Cooper, and then you have the sketchy Chinese tires.
If you can wait a couple weeks, there's also DTD's Black Friday sales