I've only sailed with
DCL so far. I've yet to be disappointed in any of my cruises. Some of them rank among my best vacations.
I've been dealing with an NCL cruise for the last year and well, pretty much everything about it has been a hassle and just felt... bad. The website is shady, the "free" offers are shady, getting my certificate to work was nearly impossible, they make you pay for port adventures way in advance, you can't easily link dining reservations to others. And, they changed 3/5 of our ports without any explanation well in advance of the cruise, but offered no compensation or refund.
So, we'll see how it goes when I finally sail in April, but so far, I'm with DCL all the way.