Do you have a preference as to the braided supply line with the plastic 7/8 in. ballcock nut that connectors to the toilet versus a metal nut instead? I was thinking the metal one might be less likely to crack?

Braided supply lines are a maintenance item like car tires and hoses, and they are known to burst with age. In my rather limited experience, the braided lines with metal nuts are overall higher quality, so I buy those when they are available. Sometimes the big box stores don't carry lines with metal nuts. Sometimes plumbing supply stores don't carry the plastic nuts.



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Every toilet fill valve I've seen has a plastic nipple and uses a plastic nut to seal it against the bottom the tank. Having a plastic nut on the braided fill line doesn't add a point of failure vs. a metal nut.

Personally I have no preference and the plastic nut works fine for me. I am not so worried about it cracking because you are supposed to tighten it by hand so very unlikely you can cause a crack by over tightening.

I have caused cracks in plastic nuts by hand simply by loosening them (toilet line) or tightening them (sink lines). I'm strong but not that strong.