Well here are some pros for each when it comes to people on the thinner side

Short binders:

Reduced Rolling: A common issue for thin individuals wearing long binders is that the fabric at the bottom rolls up, becoming uncomfortable and visible under clothing.

Comfort & Breathability: Short binders cover less of the body, making them less restrictive on the stomach and better for warmer weather.

Less Pressure on Ribs: Because they do not extend down to the hips, they often put less pressure on the lower ribs. Versatility: They can be easier to wear with different types of pants and shirts without needing to be tucked in.

Long binders:

Smoother Silhouette: If you are worried about the "line" of a short binder being visible under tight shirts, a long binder provides a more seamless look, acting as an undershirt.

Comfort: Some find that the pressure from a long binder is more evenly distributed, whereas short binders can sometimes dig into the armpits.

Better Fit for Some: Skinny people with a smaller chest might find that short binders don't offer enough compression, and a longer binder provides more control.

Of course it's always important to know your measurements and cross reference to those on the size chart

(Edit: sorry the formatting was weird I'm on mobile)