I neck size all my brass. When they get too large to chamber any more (about 5 to 7 loadings) I buy a new batch. I'm getting great accuracy, but I think it goes beyond just neck sizing. I happen to believe that the concentricity (straightness) of my ammo has a great deal to do with my results.

I started out with the Redding S type bushing neck dies. They worked okay, but concentricity was never as good as I wanted it to be. So, after listening to some other guys, I decided to try the Lee collet neck die. All I can say is, I've been totally satisfied with this die. It's easier to use because you don't have to lube your cases, but more importantly it produces very straight ammo. Runout has been virtually non-existent in my loaded ammo since switching to this die. Of course the Co-Ax press and Redding competition seaters help a heck of a lot too. Another thing I like about the Lee die is that it works the case less than conventional dies, so it actually has three distinct advantages.

But back to your question about whether or not neck dies produce more accurate ammo. Maybe so, maybe not. I'd say they certainly have the potential to. But if your whole setup (press, sizing die and seating die) isn't capable of producing consistently straight ammo, I don't think you're going to see appreciable accuracy gains with any neck die.

Just my 2 cents.