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.
yes lending bitcoin is too much risky. i think trading bitcoin is the best option. investing in ICOs in in exchanges for trading alt coins is the best option from where a person can earn a good amount of bitcoin.