If hdd capacity is holding you back, WiiU's 32gb flash memory is equivalent to PS4/XB1 500gb hdd.
If you go just with retail titles PS4/XB1 mandatory installs will fill it up fast, right? Meanwhile WiiU retail titles offer no installs and it's only the updates which are installed on your drive. That measly 32gb will last you much much longer.
If you go fully digital in both cases you need to expand the memory since it isn't enough.
If you go halfway, somewhere down the line you will need to expand your memory and it's easily done on the WiiU, you just need a usb drive. Can you expand your capacity on the PS4/XB1 or do you only have the upgrade option?
Just noticed it's all IFs, where are the ELSEs?