PS4 games: retail... so I have the option to sell them if I get the digital version later via PS+ ;)
Vita games: mostly retail for the same reason, but it depends on the price... Sly 4 was much cheaper on PSN than the retail versions. And my Memory cards are full with PS+ games anyway. ;)
PS1 + PSP classics: digital... great PSN deals and I can play them on different devices
3DS games and DS classics: I'd love to go 100% digital for several reasons:
- 3DS games aren't that big, DS games are even smaller... so many games can fit on a 32 GB SD card
- I don't want to carry several 3DS and DS moduls around... they need additional space and can be lost/stolen
What holds me back?
- the 3DS needs an account system... I don't want to lose all games if the device gets stolen or breaks... or if I want to switch to a different 3DS model. These worries about your digital purchases you don't have with any other mobile device (Vita, PSP, iOS, Android, WP8...)
- no DS and only a few SNES games in the eShop... Nintendo could make a sh*tload of money by offering the best DS games for $10 to $20 in the eShop. Offers like "Ace Attorney 1 - 4 for $29.99 or $9.99 each" would boost the fan base and sales for Ace Attorney 5.
PC games: mostly digital nowadays... I still have hundreds of PC games in DVD boxes and big boxes, but the growth of my retail collection nearly stopped. Steam sales, GOG, humble bundles (and other indie bundles) and kickstarter projects have taken over.