There is some compatibility issues with USB 1.x-2.0 machines depending upon the flash drive controller chipset, AData has a tech note about certain USB 2.0 models needing a "driver/enabler" for Win9x-ME+NT4/OS 8.x and Lexar S25(USB 3.0) has compatibility problems on USB 1.x/VIA USB 2.0 chipsets & they won't support anything lower than OS 10.1/WinXP--only found that USB 2.0 chipset incompatibility after it refused to work on my first gen Athlon 64. Other Lexar USB 2.0 flash drives seem more "friendly" on USB 1.1/VIA USB 2.0 based systems.
Beyond those two makers, SanDisk, Patriot, PNY & Kingston hasn't changed their controller chipset supplier(s). If you don't care about raw speed and prefer compatibility with OS 8.x/9x I'd recommend PNY & Kingston.
SanDisk at one point sold non-USB compliant flash drives optimized for Win8/8.1 features/Win2Go, instead of being seen as "removable" it was a "fixed drive" embedded to the firmware which made them non-bootable(Linux/USB OS X installers)/problematic on older OSes or PC OEM OS restore tools--I have three of these useless Cruzer/Cruzer Glide models, they frequently get stuck in a non-eject/unmount loop on WinXP/Vista/7/OS X Snow Leopard(and earlier) and you need to shutdown to safely remove. SanDisk took nearly 8 months to move back to their old "removable" storage firmware but stores still had "new old stock" until late 2013, SKU never changed which made identifying old(Win8/8.1) vs new impossible until you opened & plugged it in then worry about a return policy headache at stores.