I've had the pleasure to fly on both Delta and Northwest to/from Hawaii.

First, here are pictures of their meals (password for photos: flyertalk):
Delta: http://slippahs.smugmug.com/gallery/733724/2/32269551
http://slippahs.smugmug.com/gallery/733724/2/32269555
Northwest: http://slippahs.smugmug.com/gallery/733724/1/24382786
http://slippahs.smugmug.com/gallery/733724/1/24382830
(Please note, photos are not to be reproduced without written consent).

As for service, both are up to par with Delta likely being a bit friendlier. Last HNL-ATL flight I was on, one of the captains (there's three on board these flights) came out during boarding and shook everyone's hand, thanking them for flying Delta. On Northwest, however, I can 90% of the time be assured to be addressed by name and thanked for being an elite member of their airline.

Here's the difference. Leg room. Out of MSP, Northwest operates their DC-10-30 aircraft with ample leg room and almost lie-flat seating. Delta seats don't even come close. Here are pictures of the First class cabins on both airlines:

Delta: http://www.airliners.net/open.file/104076/M/
Northwest: http://www.airliners.net/open.file/411481/M/

Hand's down. For the seating, I'd go with Northwest. Delta's 767-400 seating is a bit too cramped for my tastes.

As for entertainment, with Delta, you'll have a choice of movies. With Northwest, you'll have to watch what's given to you with the rest of the plane. But on both airlines, you do get your own TV.

That said, if you're flying the ATL-OGG non-stop for Delta, they're using the 767-300ER aircraft with B/E seating...

Hope this helps.