I don't have a rule. It all depends on the game, franchise and price.
If I really trust the franchise, I usually buy digital whatever the price for convenience.
If I don't trust the game yet, like when pre-ordering a game that I don't know if I'll like it, I just buy physical, so I can return/re-sell.
When the game is discounted, I check both physical and digital prices. If it's too cheap on digital, I just go for digital. If it's cheap on both, but not really cheap on digital, I go for physical, so I can return/re-sell if I want.
Sometimes I buy both. I may pre-order physical and after checking that the game is brilliant, I just buy it again digital if the price gets discounted so I can have the convenience of not dealing with discs.
I don't give a damm about collecting, but I do buy physical once or twice a year because I liked the box art or maybe to get a collectors edition. But I rarely do that. I may have about 20 collected physical games bought in the last 15 years.
God bless You.
My Total Sales prediction for PS4 by the end of 2021: 110m+
When PS4 will hit 100m consoles sold: Before Christmas 2019
There were three ravens sat on a tree / They were as blacke as they might be / The one of them said to his mate, Where shall we our breakfast take?
