What is riskier a call or a put option?

IF you are BUYING the option, neither is necessarily more risky than the other. The longer the expiration date, the more likely the market will go up, so the call becomes more appealing. In both, the most you can loose is the premium paid. IF you are SELLING the option, selling the put is more risky. Because a stock can technically go to infinity, you have unlimited loss potential. When selling a call, you can only loose up to the value of the stock as long as the call is covered.

I just read the above ...it's backward.

Puts exercise if the share price is below the strike price, not above. You can potentially lose everything between the strike price and zero--I'm neglecting the premium for now. If you write calls, you can lose everything between the strike price and the share price. If it's a covered call, it's a paper loss, but if you write naked calls you lose real money. It depends on the writer's investment strategy.

Churners are more at risk with puts than are buy-and-hold guys. If I own a lot of stock that's at $102, believe it's really worth that, and want more of it anyway, why wouldn't I want to write a put with a seven-day expiration period at $100 with a $5 premium? This brings the price of the stock down to $95 per share, which is a great deal! Churners approach puts tactically: they subtract the premium from the expiration price. In this case, that would be $95. If they think the stock will be lower than $95, they know they can buy it from a broker cheaper so the put's a bad investment. If it's between $95 and $100, they'll use part of the premium to pay for the stock so it starts to look like a better deal.

Writing calls is either moderately risky or unbelievably insane. If you're in a covered call, all you can lose is the difference between the share price and the strike price, and that's "paper wealth" anyway. The flipside of a covered call is that it stabilizes transactional income. If you're trying to get out of a position slowly, or you've got so much of it you can afford to shed some, selling a thousand shares at $100 in a covered call means you know there will be $100,000 more in your brokerage account at the end of the deal.

A naked call--you offer to sell stocks you don't own in a transaction where "in the money" means share price is higher than strike price--is different: these are so risky a lot of investment houses won't trade in them. If you write a naked call for 10,000 shares at $100 and the stock shoots up to $140, you need to pull $400,000 out of thin air right now. If you write the same call and the stock drops to $70, you're golden: someone probably paid you $10 per share to do that.

So...as far as futures contracts go, here are the relative risk levels:

Low

Covered puts

Naked puts (slightly riskier because, as with all naked transactions, there's a chance the security won't be available when the option exercises)

Covered calls

Casino gambling

Naked calls

High