Bootable USB(not live) performance tweaks

[DrSafetyMD]

Hi. I've created a few portable Linux Mint USB sticks over the past year, meaning I actually installed the OS to the stick; these are not liveUSB's.
I've noticed a few things:

1) When the system is updating or if I'm downloading something, whatever I'm doing tends to hang for ~15 seconds every ~10 seconds. After the download is done, everything's fine again.
2) Some flash drives are faster than others.

I was wondering how I could (a) pick the best flash drive for the job and (b) tweak that flash drive to perform adequately.

I've also been doing some research on SSD alignment. Could that have something to do with it? Could USB write speed be the issue?

Thanks in advance, guys

[Minterator]

Use a USB 3.0 card reader with an SDHC UHS flash drive. That combo reads at 75MB/s & writes at 45MB/sec, so the OS will feel as fast as any hard disk. USB 2.0 will work as well, the speed of the UHS flash drive is more important.