I would buy 2 3tb drives from different manufacturers (one SATA online, one USB offline) - backup the online to the offline USB every month
Yup, I think this is the answer.
This 'which drive is best' question comes up all the time time and the answer is that you're fooling yourself (no disrespect intended to anyone) if you put any faith whatsoever in any drive by any manufacture. So I personally think that answering that X manufacturer is better than Y is giving a false sense to someone that perhaps X drives might not fail, where Y's may fail...nope, THEY ALL FAIL. Assume absolutely that, whatever you buy, it'll fail tomorrow and then you're on the path to data security.
I generally also subscribe to more smaller drives than less bigger drives, but that can get cumbersome in terms of making sure everything is frequently backed up unless you're like me in that most of the data on the small drives is not accessed often...in that case I like having smaller drives because then I don't have all my data on a single pair of drives...less info is lost if I do have a drive failure. That said, drive size isn't my main concern. As long as you keep essential data backed up, it really doesn't matter if you're committing to small or large drives, as long as redundancy and reasonably frequent backing up is the key component to your 'safety' plan.