For Nintendo and Bethesda, and a few other publishers, I buy new. I mostly vote with my wallet if I like what one of the major publishers is doing.
Otherwise, I buy used and give the money to the original owner (eBay).
EDIT: I know it's not a perfect fit, but I cover something similar in my newest YT video. See my sig for the link!
Retro Tech Select - My Youtube channel. Covers throwback consumer electronics with a focus on "vid'ya games."
Latest Video: Top 12: Best Games on the N64 - Special Features, Episode 7