Anybody know what works better for tarp tensioners; thin stretchy or thick not so stretchy?

My chiropractor brought me some surgical tubing he uses for therapy with his patients. There are two distinctly different types. One is blue and pretty stout; the other is green and more stretchy. Both are stiffer than the sling shot replacement tubing. I made a set of the blue ones last night and will make a green set tonight, but I'm wondering if there is any real difference in performance. The weight difference is slight and I'm done counting grams.....for now.

I KNOW I'm not the first one to try this. No rain forecast in the short term so I'm wondering if anybody has any comments.