Well, there are so many combinations one can do to secure their coins.
Totally 90% in Cold wallet.
7% on your harddrive on a computer.
3% on your phone. If 5% or 10% means millions for you then I'd say Gratz
I thought it was more like in the range of 5 % = 100 000 coins.

My suggestion is never keep too much on exchanges. Alot of people had lost their BTCs that way before.
With DigiBytes, you have even better reason (compare to Bitcoin) to not keep many of your coins on exchanges. Because the transaction is so fast, you just send them there when you need them, and be able to trade within 5 mins.
I haven't used paperwallet before. So I don't have any comment on that matter.
USBs are so cheap to get.