Lead is the preference,,,with pipe flashings such as the plastic or the aluminum ,,,the fastener (Fastened or not)(Clips or no clips) is the last thing IMO to fail with those types of flashings.What makes a plastic or aluminum flashing fail more times than not is the neo collar.Dry rot of the rubber from extreme exposure resulting in cracking and splitting around the pipe itself is where the product fails.
In Missouri our squirrels have an appetite for lead.The little goobers gnaw and chew the lead around the tops exposing the pipes and overtime will cause leaks.But I would much rather have a squirrel cause the leak than me being a cheap skate and trying to provide a 10 yr. workmanship warranty around a product that will fail in a matter of a couple years depending on the severity of summer time temps.
I really like Perma Boot,, A little pricey but looks really good.I can spend about $4 for a 2""-3" plastic flashing,,,$6 for an aluminum 2"-3"''$15 for a lead 2"-5" or $20 for a Perma Boot.
Anyway you look at it Lead or Perma Boot is a better investment.It makes more sense to me to provide a better product for the customer than pocket a few bucks per flashing.
I don't think any of the top 100 roofing companies in the United States can say they made millions by shaving cost using an inferior product like plastic or aluminum pipe flashings.