Barcode scanner hardware - selection suggestion required

I would like to buy a barcode scanner that will read out the shipping agents’ bar codes (dhl, fedex, and ups).
These agents pre-print the bar-codes and give it to the business houses to prepare a shipping parcel.

My customer’s parcels are at least 20+kgs and probably stay away from computers.
Even a 7 feet long usb wire does not work.

Most importantly, it seems that there are a lot varieties of barcode scanners.
Which model should I prefer to buy to read out those numbers?
Which categories of barcodes are used by those shipping agents?