Gus's bowls are ceramic and Charlie's and Ace's are metal. And Gus, who does NOT use a plastic bowl, DOES have a pink nose! His nose darkened back up last summer, got pink again this winter, and I am sure it will darken again this summer (though it won't get back to coal black).
Some feel that plastic bowls can trigger an allergic reaction that can discolor your golden's nose--creating that "dudley nose" which is a pinkish nose in goldens--which is a fault.
If you were to run a poll, I'd venture to guess that the overwhelming choice would be stainless steel (metal). Easy to disinfect and clean.
Maggie's nose is pinkening, and she has only had stainless steel bowls since the day we brought her home (and she's from an Amish Puppymill, so I don't think they used plastic bowls, either, though I didn't see her bowls.)
I use ceramic bowls in the house (food and water - they are washed each use; same bowls mentioned above by Cathyjobray) and use Stainless Steel outside for their water while in the dog yard.
The SS water buckets are washed a few times a week and can better withstand being banged around by goldens flying around Still shiny after all these years.
My Rowdy would not eat out of plastic bowls - period. Even if it was steak he would not touch anything that came in plastic or perhaps more interestedly, that had been in plastic. He was the dog who taught me so much about allergies.