KJV, LSB, NSB are the Big 3 for everyday reformed Christians. For deeper work, NASB95+Septuagint+NT in original Greek.

They have all been altered. That makes me sceptical.

My preference for English: ESV For Spanish: Reina Valera de 1960

The one you read .

This may be a lot more info than you are interested in, but here are my thoughts in as condensed of a way as I can put them. Also, full disclosure, I work for Crossway which created and publishes the ESV translation: I'm not sure what you mean by *best* but what I would argue the best thing you can...