Would you keep your paper money in other peoples wallet? I don't think so.
If you keep your "paper money" in a bank, it's sitting in an online wallet. There are no private keys for paper money, only the paper money...so if it's not literally in your possession, you don't own it.Bank IS safest way for keeping your money and you own it. It is your money.
You can compare it like this:
Bank(paper money) - hardware wallet(bitcoin)
Your wallet(paper money) - online wallet(bitcoin)
Other peoples wallet(paper money) - freebitco.in(bitcoin)
It's my opinion about freebitcoin as wallet, i still like faucet and lottery
If you read the posts then you will see that it is the opinion of most of the members here. Its not a good thing to store your BTC in these exchanges regardless of how much interest they are going to give. Its just not worth it, and Banks are the safest place actually to keep your money and get some interest at least.