Only the 64GB choice you need to think about. While it is theoretically possible, most 64GB sticks seem to require you to format it in exFAT or NTFS. If you will be plugging the stick in non-Windows OS, that will be one concern.
Is speed (in particular write speed) important? If yes, then you can skip all the cheap ones and concentrate on the ones that have speeds listed. You can also use reviews to find out that information.
Another criteria is USB 3.0 support. Generally they are faster, but if 2.0 is still important to you, then you will need to look at their speeds under 2.0 as well.
Then, comes the different "form factors". Generally they can be grouped into these:
- stick with a cap, then you need to see if the cap is separate, and/or if the cap can be put on the stick even when plugged in. For example, my old Kingston allowed the cap to be plugged into the back of the stick so I won't lose it.
- the "swing style" cap less design, example
- the "retractable" style, example
- mini port style, usually quite rugged because the enclosure surrounds the contacts, example
- mini with exposed contacts, example
There are some practical concerns choosing one over another, but ultimately it is a bit personal.
And then, there is the shell material, metal vs platic.
In terms of brands, Kingston and Sandisk seem to be the biggest brands, then you get Patriot and a whole bunch of Taiwanese makers like A-Data, Transcend, etc. Then you have a whole bunch of off brands. Difference is usually length of warranty (seriously, do you care about these "new floppies"?) and price.
Last but not least, there is price. Always look for coupon codes, promotions, and deals.
IMO: the sweetspot now is 16 or 32.