There are not singing waiters on NCL. They used to have one or two "dining room shows" each cruise but with Freestyle they no longer do. I personally like the that it is no longer part of the dining experience. I am not a big fan of it but many cruisers do love it.
Please don't rule out NCL because of the lack of singing waiters. Add $100 to your cruise budget, experience all of the alternative restaurants and you will have a great time.
Then again, you won't make a bad choice if you go with Carnival. I head out on the Carnival Pride in just over a month.