Discs if it has a disc, DL if it's digital only game.
With discs, you can always sell it back if it;'s a console game. Stores never take PC disc games so going DL only isn't a big deal. And just like the old days, few people want to risk buying a PC game used.
I see myself buying less digital XBL/Indie games though. There's no mandatory demo/trial for them, so I won't bother unless I see it for a 75% cheap deal or I know it's a good game to get. I bought lots of XBL and Indie game based on testing out the demo first. Without that, I won't bother, especially with ultra low budget Indie games which probably have a 10% good/90% garbage rate.