Hard-copy all the way!
1- I have a brother who also owns a WiiU. So we both talk to each and buy different games, with the exemptions of those ones where we can play multiplayer, specially co-op. So it's a no brainier we can exchange games whenever we see each other.
2.- There are always better sales and discounts, so far, of CDs than eshop games...if sometime in the future eshop becomes something like, say, steam, maybe just then I will fully commit. but as I said in # 1, I won't be able to exchange games with my brother, but if eshop games have huge discounts, then we can both buy more games!
3.- As the guy in 1st post said, I can always sell my games...I have been very successful selling my used games, I usually know when and how to sell them. I don't sell many games, as I am very picky and buy always the best, but year franchises like Call of Duty get useless quite fast as the new releases come so I sell them after a year or so.
I have 12 WiiU CDs so far and plan to buy more. I only buy digitally VC games and indies. And I have make the most of my purchases by buying most of my games at a discount.