What should a beginner focus on first: developing pieces quickly or trying to attack right away?

Beginners should focus on developing their pieces quickly and controlling the center before trying to attack. Strong attacks only work when your pieces are active and coordinated.

Do you have a different opinion on this?

You generally want to be quickly developing your pieces and controlling the center before trying to attack... and this applies to all rating levels. Higher rated players develop a better sense into when those few exceptions are, but usually you'll want to keep developing until there's the potential for an attack and only then might you choose to begin your attack.

Which is correct depends on the position.

Chess Openings Resources for Beginners and Beyond…

https://www.chess.com/blog/RussBell/openings-resources-for-beginners-and-beyond

There are no different opinions on this. Attacks don't happen without development--or without incredible stupidity and carelessness on the part of one's opponent.