Underwear that's actually good for varicocele needs to have the following 3 benefits:
Provide Maximum Cooling (Fabric)
Create Penis/Scrotum Separation (Design)
Provides Compression With Cooling (Compressive Scrotal Support)
Most scrotal supporters are not good for varicocele/your testicles because they over-heat your testicles. You must combine scrotal support with cooling to attain any real benefits. Compression naturally helps drain the varicocele. Maximum cooling helps improve testicular health & couteract the over-heating effect of varicocele.
Be very cautious, most underwear actually over-heat your testicles. What you need is underwear that's provides maximally breathable and cooling. As well, if you want the best underwear for your testicles, they should also provide some testicular support.