Broke my first glass carboy in over 10 years of brewing, fell into the glass and did my ER penance. I need one or two more reasons to pop for the ss conical over the plastic. I'd appreciate your opinions. Bill
Plastic: Cheaper, lighter, can scratch
Stainless: more expensive (though some of the newer options get you closer), more durable, sanitary fittings are an option, many can be pressurized enough transfer, no o2 ingress.
I guess I would try to figure out how long people are using the plastic ones before they decide to replace them due to scratches or staining. If you need to replace them 3 times during your brewing career, stainless is looking good from a cost POV and other than the weight is better in every other way.