I'm an ebay seller and am very particular on my packaging. Someone once told me "Good packaging isn't cheap, but cheap packaging isn't good either".
I use only Scotch 3M packing tape. I've tried them all and this is the very best, not the cheapest, but in the long run I use much less than the other brands.
I usually buy the six pack from Sam's Club for $15.63 which is the best buy anywhere. The tape is 1.88" wide x 54.6 yards for a total of 327 yards according to the label I have here in front of me. I like this tape, it's strong, thicker than any other brand and doesn't yellow with age.
I not only use this for my ebay packages but for everything around the house, Christmas storage boxes to picking up dog hair from the couch. I would highly recommend this to anyone, especially ebay sellers.