Plastic is actually plastics. Correct blend of plastics has an OK reputation with todays fuels. Slightly wrong blend of plastic will call for revisit. Brass will stand the test of time and fuel additives, whether its common pump gas or ethanol free. Ever heard "We get what we pay for"? In most cases its true. A quality brass float would cost you more coin but would cause you less grief. Nobody will have anything bad to say about a brass float other than the thickness of the brass used today and eventual cracking. Neither is going to last forever. Nothing does.
I replaced a brass float that had cracked right where the steel wire ring retainer ended. I didn't dare to replace it with a "who know what" recycled plastics coming out of China today. Good luck is all have left