I think gambling and Altcoin giveaways are a very good source of bitcoins. And once you have enough free bitcoin then start lending them.
Lending is not reliable source of bitcoins at all. It depends on pure luck and you can lose. With lending it's almost certain that you will lose some amount too. I would vote for trading, it's also risky but there are some rules and also selling your intellectual skills and services for bitcoins.
Lending is risky because of peolple. Don't let your personal finance in other people hands, try to be you who risks your money and win or loss without blame.