I have been struggling with USB card readers since I switched to using RAW files. When trying to transfer large amounts (~4 to 8 GB) of image files from an SDCard in a reader, to my computer, it would get part of the way, and would give an error and disconnect the card/reader. I would have to remove it and plug it back in, then transfer the remaining files. I tried 2 different card readers, one purchased very recently. All of them USB2 (because that's all my computer has) and both cheap brands.

I can transfer the same files without error, by putting the card back in my camera, and plugging it into the USB port, but that's a bit slower. So, today I bought a newer cardreader. Not a big name brand - it's a Digitech, but it's a USB3 reader, so newer design, supports SDXC to 2TB etc etc., and still only cost $15.

Works perfectly!

So, looks like the older generation cheap readers don't fare too well when pushed hard. Thought I'd mention this one, in case someone is having trouble, or is just looking for a card reader at a good price. (am I allowed to post a link to the where I got it?)