i prefer natural quartz crystal balls, but that's just me. i like things closest to the source. natural quartz will have inclusions. one with the least amount of inclusions or cloudiness would be considered superior. i buy most of my stones from a private rock hound/collector, so i know more-or-less how they were harvested and that the least amount of harm was done to the earth.
you can scry with alot of things. before buying a ball, you might want to try scrying with a bowl full of water. choose a very dark bowl (not plastic). i prefer to use rain, spring or other natural source of water, rather than tap water.
when scrying, i prefer to use indirect or low lighting. seeing a candle flame through or reflecting on the ball, is such a strong image, that for me it distracts, rather than enhances the experience.
after asking for assistance from my guides, grounding and connecting, i let go and allow. the images happen.
i think trying to see and expecting to see certain things, like fogs or hazes, interferes with the process.
i must not allow myself to try to analyze what i am seeing, to put a name to it, or to figure out what it symbolizes, or it is gone. i have to just open up and allow it.
at some point the image and.... can't find the word, but it is closest to a vision, that is sort of inside my head......... merge and become one. the ball is no longer separate from my thoughts, if that makes any sense it all.
i only begin to think about what i've seen, after i am finished.
hope this helps!