Not on that sector but I flew JFK-CPH last year in economy and just flew MAD-JFK in premium cabin.
For economy, I prefer LEVEL over Norwegian because LEVEL's cloth seats were more comfortable over Norwegian's hard leather seats. While I like 787's air pressure that helps with jetlag, I think A330's 2-4-2 seating is wider than 787's 3-3-3 seating. Norwegian was very strict with the carry on bags. Norwegian's free entertainment is a plus. LEVEL I think will only offer free entertainment until June/July. I noticed that Norwegian's fares have been creeping up so it is not as attractive in economy as it used to be. Now their premium cabin...

I think is fantastic. The fare difference was only like $60 between economy and premium cabin on the MAD-JFK flight I just took so it was no brainer. The experience was premium throughout: complimentary seat selection, premium check in line, premium boarding call and the best part is the seat itself. Sure they are only recliners in 2-3-2 config. but they are large and comfortable. They provided 2 full meal services, free alcohol and drinks, etc. They provide nice blanket but no pillow. The cabin crew is friendly although their moral isn't so high b/c management is not making the right decisions. I hope they stay afloat because I really enjoyed the premium cabin experience given the very reasonable price.