New Costco 14TB vs Refurb 18TB, which one would you get?

I'm building a NAS and trying to decide between drives. I've never done this before, most of my data is on google drive and a few externals. I bought a few drives on BF deals and trying to decide which ones to keep.

Costco Seagate 14TB External ($149.99) pros:

• Actually new
• Costco "unlimited" return policy/warranty (will most likely be around longer than goharddrive, and if a drive dies I can swap it for a new one within a few hours)
• Possibly quieter? I haven't shucked them yet but I've heard these use ironwolfs and they're quieter than exos

Ebay Refurb 18TB ($169.99) pros:

• more space per drive
• better cost/TB ($9.44 vs. $10.71)
• 5 year warranty (without possible guilt of taking advantage of costco)

Given these choices, which would you more experienced data hoarders choose? I have space in my case for 8 drives and won't need that many for years if ever.

Also, trying to decide whether to use ZFS or not. I like the idea of bitrot protection and extra speed once I eventually upgrade to 10gbe, but am very concerned about noise from running the whole array 24/7.