All silicone oils should be the same quality, as they are supposedly 100% silicone oil, the only difference is the viscosity, and the way it is measured.
"weight" or "w" is not a recognised international standard, there is no standard for measuring what viscosity 30w silicone oil is, it's up to the manufacturers to decide what to put on the bottle. So if using oils sold as "weight" its best to stick to the same brand, otherwise tuning shocks and diffs becomes confusing.
For example, Brand X's 30w, could be the same as Brand Y's 35w and Brand Z's 25w.
I prefer buying oils in CPS, as its an recognised international standard, with standard ways of measuring the viscosity. So Brand X's 500cps, should be very close to Brand Y and Z's 500cps.