I have an opportunity to buy a Precor 546 that is 3 years old that has been refurbished for $1000.
I have also looked at the Schwinn 418 for $500 and the Nordic Track 1300 for $800. These are at my local Costco. I was considering them because of their generous return policy.

Would you buy the used one because it was originally better quality or the others because they're new?

Or.....something else altogether?

Any and all advice is welcomed!

Oooh, that is an interesting choice, and it sounds like you'll have a fantastic piece of equipment either way Is the refurbished Precor coming from a store, or an individual? Is there a repair warranty with it, or will it be purchased "as is", without a warranty?

The Schwinn 418 was rated a Best Buy by Consumer Reports, and that's with the original retail price of $1,000. They commented "Very good overall performance and better quality than the other moderately priced models we tested." They didn't rate Nordic Track. They rated a Precor highest, but it wasn't the model you are looking at.