Well, we keep using these and running out. Finally settled on a high, medium and low mix strategy:

## Low mix

USB 3.0 keys that are bullet proof and that can live on a key ring. They aren't super fast, but they are tough. The two contenders are the Kingston SE9 G2 which is decent on read and pathetic on writes particularly the real world random writes:
Sequential Write : 16.539 MB/s
Random Read 512KB : 115.531 MB/s
Random Write 512KB : 0.541 MB/s
Random Read 4KB (QD=1) : 12.891 MB/s [ 3147.2 IOPS]
Random Write 4KB (QD=1) : 0.006 MB/s [ 1.6 IOPS]
Random Read 4KB (QD=32) : 8.340 MB/s [ 2036.2 IOPS]
Random Write 4KB (QD=32) : 0.010 MB/s [ 2.3 IOPS]
As a comparison a good but big USB key is the SanDisk Extreme with speeds like which is 2x faster on reads, but literally 100x faster on 4KB random writes.
Sequential Write : 61.457 MB/s
Random Read 512KB : 185.310 MB/s
Random Write 512KB : 6.704 MB/s
Random Read 4KB (QD=1) : 7.545 MB/s [ 1842.1 IOPS]
Random Write 4KB (QD=1) : 5.313 MB/s [ 1297.1 IOPS]
Random Read 4KB (QD=32) : 9.004 MB/s [ 2198.3 IOPS]
Random Write 4KB (QD=32) : 2.372 MB/s [ 579.1 IOPS]
But it is still 2-3x faster than it's nearest competitor the Silicon Power Jewel
Sequential Write: 10MB/s
## Medium Mix
This is where you do need speed for things like booting, but don't care about size. I normally use this for creating operating system setup. Here the best combination is a fast SD with a USB 3.0 to SD reader. This can double as a camera SD card as well. With the SanDisk Extreme Pro leading the way along with a good USB 3.0 to SD system. The big advantage here is write speed and flexibility as it can be more than a USB
If speed is a relative issue, then you can use a Sandisk MicroSD which runs at 48MBps and 35MBps sequential write (slower reads, but much faster writes). This is super flexible as if let's you also use this in a cell phone or raspberry pi, or a camera or as a boot disk.
If you want something a little faster, then then you have to get a true SanDisk Extreme Pro SD 64GB for $55 if you need something industrial strength 90.21 MB/s read and 81.06 MB/s sequential write Or a PNY Elite at$27 is a very good buy although Newegg folks like it a bit less for reliability which is about double the speed at 90MBps read and 70MBps sequential write. The big advantage compared with the low mix is the sequential write and the flexibility of a SD card although it is bulky
CrystalDiskMark 3.0.3 x64, using built in laptop card reader:
Seq Write: 67.89 MB/s
512K random write: 23.27 MB/s
4K random write: 0.677 MB/s
4K QD32 random read: 5.585 MB/s
4K QD32 random write: 0.612 MB/
## High Mix
Here you get a USB 3.0 to SATA converter and plug in a real high performance SSD drive like the Samsung Evo 850 which should give you 400MBps read and write. The main thing you need is to make sure your computer motherboard supports UASP. This is most useful for using it like an extra hard disk where you need some more storage in the field as in a photo shoot or where you want to do a backup. Note that SSDs are do need power applied. They will lose their data if they don't have power, so if you want true archival, you need to use a HDD. This works really well with ASUS motherboards if you enable it.
The main thing is that you have to make sure UASP (USB Attached SCSI Protocol) is supported on your motherboard *and you have turned it on!*

• You also need an operating system that supports it, which is right now Windows 8, Mac OS X 10.8 and it is disabled and buggy on Linux.
• You then need a compatible USB controller like a late model ASMedia 1042 or late model Reneses
• Then you need a motherboard manufacturer to pay for the license and implement it.
• USB to SATA controller that supports UASP like the \$12 Startech for the same dollars something with an Sabrent enclosure

Servedbyhome.com did find that it increase performance by 50% for sequential reads and writes so they were getting 300MBps read and 200MBps writes out of USB 3.0 compared with a theoretical 500MBps, so not bad. So for instance on a P8Z77-I (which we have), it needs a tickle with the USB Boost. ASUS added this years ago (2010?!) for their systems through their USB Boost and Gigabyte says they do, but can't figure out if ASRock does.
Tom's Hardware also did a good review of this and just short of UASP is turbo which increase the data transfer size on USB. The short answer is ASUS Turbo definitely does.  For ASRock XFast USB makes things better or you can just hack the registry and at least some motherboards like the ASRock Z97 Killer support UASP but others like the ASRock Z97 Extreme6 don't