It's a matter of preferrence and what it will be used for.
The urethanes are more technical and less open time. They do not like water, it causes foaming.
PR is less technical and open time can vary depending on many factors. It will tolerate water based paints if you choose to use that for a colorant. I've had water leak into the container when warming in a bath. The water just floats to the top.
As for translucency, when casting, it will also depend on several factors. I occasionally still get some translucency in spots, but not often. I do paint the blanks irregardless. Always best to be safe.
If you do decide to cast...
Make sure to read the MSDS on the materials you use and understand ALL of the DANGERS. Not just the resins, but the pigments, dyes, catalyst, etc. all pose some level of toxin risk.
Most people don't fully research casting and if the materials are mishandled and the proper precautions not followed, there will be a price......
Is your health... or even your life... worth taking shortcuts??
Cast SAFE!