Best material for a working prototype?

[JohnWilkerson 0]

I have a part I'm needing to print.  The material must be very strong but I need it to have a slight flex for a rope to release through. Picture is just an example I pulled from Thingiverse.

It will be similar to how this works.  I am using an Ultimaker S5 Pro Bundle

[MariMakes 199]

Hey @JohnWilkerson,

 

Personally I use PLA for a prototype and move to a different material if it breaks. 

Will it be used outside and will it be wet? 

You can also consider taking a glass or carbon fiber filled composite. 
You can read more about it here:
https://ultimaker.com/learn/glass-vs-carbon-fiber-composite-3d-printing-materials

[JohnWilkerson 0]

It will be used outdoors so the elements are a concern. 

[MariMakes 199]

I have a Balcony Garden made with PVC pipes. 
They need to hold the weight of the plants, and the water and are attached with a tiewrap. 

I've printed these in Nylon and some TPU for grip. 
This Nylon has hold up for 2.5 years now and has not failed me yet.