You may have noticed that some online companies tout that their fences are thicker or stronger than their rivals but this doesn't mean they are necessarily better? The true measure of a vinyl product is how well it performs over time. Is it correctly engineered to withstand the elements and impacts of normal (and sometimes abnormal) everyday use.
The truth is that most major manufacturers (but not all) comply with ASTM shared industry standards. The recipe of what actually goes into a vinyl fence or railing can be much more important than the thickness. Some companies use their scraps from the manufacture of windows and siding called "regrind" to make their fences.
One of the most expensive ingredients in vinyl are the impact modifiers and the U.V. inhibitors that protect form solar radiation breakdown. A fence can actually be stronger (more rigid) and also be more brittle and more breakable. The thickness of a body of a car does not make it a better car. The total engineering for continued performance over time does.
Bufftech who has been manufacturing vinyl for over 30 years now and Certainteed who has been backing products for over 100 years are an excellent combination for dependability you can count on. If your vinyl fence is being manufactured in India or China it may not have the same quality, dependability or accountability. Likewise, if it's a new company they might not be around when you need them.
If you buy from your local chain home improvement store, they may not carry that same vinyl fencing line when you need to expand your project or replace a damaged section.