I haven't used money gram for any transaction whatsoever, although I have heard several people stories about their experiences with it and how good it is but if it's Western Union, I have actually used it a couple of times and it's quite good as well. Although, it wasn't to buy anything that I had to make use of Western Union, but rather to receive money across from another country, I think my first ever transaction with them was around a payment of $100 in which they had to charge me around $10 for the service rendered .
My money processor is PayPal. I haven't tried Money Gram or Western.Union. For me PayPal is already trsted and proven. I have been using it for 6 years now
If you cannot use paypal or credit cad, using western union and momney gram can be a good option. Howeve,r you have to take a lot of care in using these services for buying items. You need to check the seller and find out whether he is a scammer or not.