I would consider them equal. All EU airlines must meet the same if not even more stringent standards as US airlines.

Norwegian has newer planes with new technology. However whilst new technology means safety improvements it can also mean more to go wrong.

BA has old aircraft, but they have owned and maintained them from new and know every inch of them.

Still, I will admit its comforting when you hear the fairly distinctive voice of an ex-military pilot on BA. I'd imagine there's more of them at BA than there are at Norwegian.