I hardly buy from any website on pre paid basis unless it is Flipkart (there is no incentive-COD and pre apy same price). Letsbuy sometimes lured by discount I have bought on pre paid basis.
Ebay also for low value items it is ok on prepsaid basis. I have bought on various occasions from Snapdeal at bargain prices on COD.
Two weeks ago I ordered Micromax Q6 on COD with Seventy MM at a great price with some coupon. All other sites are quoting at least Rs 500 more. Sincer it is cOD, some one called me to confirm and said it will be shipped in 10 days time. No infoabout ASWB no etc. I got a mail saying item shipped on 10th day with out any web tracking or courier info. But Aramex delivery man called me few days later, "Keep money ready, I am coming now". Got the phone in sealed condition.packing not that great like Flipkart/letsbuy/snapdeal. but ok.
I will recommend seventy mm on COD basis if the price is cheaper than others. You need to wait average 7-13 days for the parcel to be in your hand!!