I think you surely pick Amazon here. Only research focused role I see, and has faang prestige. Opti would have been best if it was qr I think, but swe is not worth it considering your goal. AMD is nice esp w RO, but data infra isn't as good for pure ML focus from what I am seeing. Tiktok and Kensho are good options but MLE focused. I have also heard from people that tiktok RO is pretty high, but idk about that myself