All three payment options are very safe. You can check their SSL certificates on the payment pages to be absolutely sure. I find Google the most convenient, but Paypal gives you the choice between converting your currency and simply letting your CC handle that - good for if you know whether or not your bank's exchange rate is better than PayPal's.

If you buy from the Humble Bundle, a man will knock on your door. When you answer it he will ask you a question. The question will be one of three - the possible answers are "time", "yes" and "nothing". Listen carefully to the question he asks and give him one of the answers. He will then tell you to go with him; do so. Lock the door behind you. He will take you to a boat which you will take to a nearby island. Whilst on the boat the man will give you something, put this in your pocket and do not lose it. When you reach the island, you will need to trek three days to the summit of the mountain in the middle of the island. There you will meet a cat who will ask you for a gift; reach into your pocket and give to him the gift the man gave to you while you were on the boat. He will then ask you three questions; listen carefully to these questions and answer them as best you can. The man will then arrive to take you home. When you get there, you will know your purpose.

If this sounds safe to you, then I daresay you are ready for the challenge. Take up thy wallet. Do not fail us.

Is that regionally restricted? I see it works in UK and Brazil, but noone came to my house in Czech Republic :-/

He did. You didn't answer.

Damn, that does explain the knocking.