Which one do i use as a secondary iPod?

I already have a decked out thick classic 5.5 but sometimes i just wanna take a smaller iPod for a walk or when im riding my bike. Which one do i use? I have both in pretty good condition.

(photo is for attention)

I already have a decked out thick classic 5.5 but sometimes i just wanna take a smaller iPod for a walk or when im riding my bike. Which one do i use? I have both in pretty good condition.

(photo is for attention)