I flew Norwegian, United and Iceland Air. Iceland Air was the best but not the cheapest (still pretty cheap tho). United has a lot of hiccups for some reason. Bad experience. Norwegian was good for what I paid, but be ready to not have any amenities at all. I was also worried they would be super strict with carry on luggage. They kind of were. Their terminal was very very crowded and food on flight only for purchase. However, I didn’t mind as I was saving a little. Others that are used to comforts might have had an issue.
As for the low cost airlines they can be a hit or miss. Be prepared for any issues to crop up very easily.