Hii
if, you are a buyer, then only the domain and price matters.
as either or both, are qualified to handle the transaction.
i have sold domains on both and didn't have any issues.
however, all sellers may not list their names on both platforms, so if you're browsing by marketplace, rather than searching by typing domains in address bar or whois,
then circumstances, platform and means of negotiating may be different.
as for "premium", if you read about premium names being sold, then all you have to do is see where they were purchased.
that, in itself should answer such questions.
imo...