If you much prefer to get the new Samsung Galaxy S8 and S8+ flagships factory unlocked, with Samsung USA warranty and in new condition, there are now in-stock and shipping in limited quantities at the Samsung USA website. The S8 goes for $725 while the S8+ goes for $825.
It is also available for purchase through Samsung Financing on 24-month installment plans with 0% APR on approved credit.
They are also shipping from B&H Photo. The S8 goes for $800 while the S8+ goes for $900.
NOTE that with previous models (eg Galaxy S7), Samsung did not prioritize updates for the unlocked phones. For example, the S7 only just now is getting Nougat (7.0, not even the latest).