Pros and Cons of using HDD or USB Flash drive (script mining)? Could someone share his/her experience of using USB flash drive over HDD?

I know that the only purpose of both is to store the OS. I am going to use Ubuntu 13.10 which I believe will fit 8 GB USB since it is said to required 5 GB free space.

I am looking for best practices of choosing USB flash drive since like storage and speed requirements(brand may be) and is there any factors (like not enough storage for update/performance/burn/block that can make it clever to chose the HDD instead.
It's best to choose the HDD because it's easier (all computers should have one), and faster than the USB drive in most cases. But it shouldn't really matter.

Why it doesn't matter

Mining is not storage intensive, you aren't storing massive amounts of data when mining. You aren't even storing data when mining. It's all stored in computer memory, think RAM. A faster storage could only help with downloading the block chain in faster time, which won't improve your mining as it is only done once and finally. 

But don't go buying up RAM as well. You mainly mine Scrypt coins with a graphics card and those have plenty of on-board memory. And if you are CPU mining you shouldn't be.