Frankly Post Office money orders are a pain to use. First, a trip to the bank to stand in line to get the cash (amount of the transaction usually exceeds the daily ATM limit). Now drive to the Post Office which is the other end of town in the downtown area where parking is scarce. Then another 15-30 minutes in line at the post office to get the PO, fill it out, and mail it (they always have one less window open than they need). There goes a couple hours of my day.
Since PayPal is out for many transactions I mostly look for vendors who accept credit cards. I’ve passed on some nice buys with vendors who don’t. Some who do charge a fee to use a card, and I will often pass on those too unless it’s something I really want and the price with the added fee is still reasonable.
Credit cards are by far the safest and easiest way to pay. I have even had to go to my credit card company to resolve a PayPal dispute when PayPal didn’t live up to their end. That’s also when I learned that dealing with PayPal over a disputed charge is extremely difficult and can take close to a year to get any action. I only use them now for transactions of small amounts.