Try saying that three times fast. Here is the scoop. USB 3.0 is very fast. I can be faster than a hard disk. You can get speeds up but it depends on first having a USB 3.0 controller on your computer. Only the latest macs and the latest pcs have it. Right now 32GB seems to be the pricing sweet spot.
But if you do then the flash drive makes a difference. Not all USB 3.0 drives are created equal.
Some are outrageously expensive like the Kingston hyper x. This is an 8 channel device and can theoretically read at 225mBps. That's much faster than most 7200 rpm hard drives. Probably 2x the best ones. But it is insanely expensive. About $2-3 per GB. Same with the Lexar Triton 16gb. I is$44 but reads at 145MBps and writes at 110MBps. There is something called super speed USB 3.0 that allows it to go up to 155MBps write.
Species the Sandisk extreme seems like the value leader with reads at 145 and writes at 90 at a $17 for a 16GB drive but there are lots of complaints on amazon about formatting and not being recognized properly. Much more reasonable are four channel devices. For instance the Adata N005 is just$24 for a 16gb unit and can read at 125mBps. That's a great way to boot your device from flash.
The two channel adata s102 pro is just $16 so way less but is 100MBps read and only 25MBps write and just$26 (Adorama) for 32GB (the pricing sweet spot).
As a comparison a low cost USB 2.0 drive like the Kingston se9 is just $10 for 16GB. But it's max speed is more like 20MBps read and much slower in write For SD cards, the big news is the move to UHS-1 which is 50MBps or more in read and write compared with Class 10 with is more like 10MBps. Classes in SD are pretty easy to understand Class 4 means 4MBps, Class 2 means 2MBps. The other change is the move to SDXC which breaks the 32GB limit for SDHC but is otherwise the same. Very useful for high speed camcorders. Pricing sweetspot though seems to be at 32GB. The highest rated on Amazon is the Sandisk Extreme SDHC UHS-1 32GB at$33 running at 45MBps, but one review liked the slightly lower priced Transcend. I've used both vendors for cameras.