Checks require trust on BOTH sides. The recipient has to trust you actually have the funds in your account, that it's actually your account, etc. - or they are burned for a NSF/fraudulent check fee. The sender (you) has to trust the recipient won't take the routing and account #s on the check and ACH some money away. Only pay via check to trusted parties.
Money orders you generally have no recourse if you get scammed. However, US Postal Service money orders are generally considered somewhat more secure, as a scammer getting paid in USPS MOs means they are committing *Federal* mail fraud, and USPS Postal Inspectors can and will hunt down people committing mail fraud.
For Craigslist and other similar buyer/seller matching sites, there is no way to track the reputation of the seller as there is no feedback system like heat/eBay/forum feedback. Therefore you should only buy/sell in person* and in cash.
One caveat about the in person - you should always insist on meeting in a parking lot of a big box store or some other place with video surveillance in broad daylight - people can and will agree to your asking price for high ticket items like laptops, TVs, etc. - only to get overly trusting sellers to go to a location where armed robbers lie in wait.